vdpa: Follow kdoc comment style

Follow comment style mentioned in the Writing kernel-doc document [1].

Following warnings are fixed.
$ scripts/kernel-doc -v -none include/linux/vdpa.h
include/linux/vdpa.h:11: warning: missing initial short description on line:
 * vDPA callback definition.
include/linux/vdpa.h:11: info: Scanning doc for vDPA
include/linux/vdpa.h:15: warning: cannot understand function prototype: 'struct vdpa_callback '
include/linux/vdpa.h:21: warning: missing initial short description on line:
 * vDPA notification area
include/linux/vdpa.h:21: info: Scanning doc for vDPA
include/linux/vdpa.h:25: warning: cannot understand function prototype: 'struct vdpa_notification_area '
include/linux/vdpa.h:31: warning: missing initial short description on line:
 * vDPA vq_state definition
include/linux/vdpa.h:31: info: Scanning doc for vDPA
include/linux/vdpa.h:34: warning: cannot understand function prototype: 'struct vdpa_vq_state '
include/linux/vdpa.h:41: info: Scanning doc for vDPA device
include/linux/vdpa.h:51: warning: cannot understand function prototype: 'struct vdpa_device '
include/linux/vdpa.h:62: info: Scanning doc for vDPA IOVA range
include/linux/vdpa.h:66: warning: cannot understand function prototype: 'struct vdpa_iova_range '
include/linux/vdpa.h:72: info: Scanning doc for vDPA_config_ops
include/linux/vdpa.h:203: warning: cannot understand function prototype: 'struct vdpa_config_ops '
include/linux/vdpa.h:270: info: Scanning doc for vdpa_driver
include/linux/vdpa.h:275: warning: cannot understand function prototype: 'struct vdpa_driver '
include/linux/vdpa.h:347: info: Scanning doc for vdpa_mgmtdev_ops
include/linux/vdpa.h:360: warning: cannot understand function prototype: 'struct vdpa_mgmtdev_ops '

After this fix:

scripts/kernel-doc -v -none include/linux/vdpa.h
include/linux/vdpa.h:11: info: Scanning doc for struct vdpa_calllback
include/linux/vdpa.h:21: info: Scanning doc for struct vdpa_notification_area
include/linux/vdpa.h:31: info: Scanning doc for struct vdpa_vq_state
include/linux/vdpa.h:41: info: Scanning doc for struct vdpa_device
include/linux/vdpa.h:62: info: Scanning doc for struct vdpa_iova_range
include/linux/vdpa.h:72: info: Scanning doc for struct vdpa_config_ops
include/linux/vdpa.h:270: info: Scanning doc for struct vdpa_driver
include/linux/vdpa.h:347: info: Scanning doc for struct vdpa_mgmtdev_ops

[1] https://www.kernel.org/doc/html/latest/doc-guide/kernel-doc.htmlSigned-off-by: Parav Pandit <parav@nvidia.com>
Reviewed-by: Eli Cohen <elic@nvidia.com>
Link: https://lore.kernel.org/r/20210406170457.98481-2-parav@nvidia.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>

include/linux/vdpa.h

@@ -8,7 +8,7 @@
 #include <linux/vhost_iotlb.h>
 
 /**
- * vDPA callback definition.
+ * struct vdpa_calllback - vDPA callback definition.
  * @callback: interrupt callback function
  * @private: the data passed to the callback function
  */
@@ -18,7 +18,7 @@ struct vdpa_callback {
 };
 
 /**
- * vDPA notification area
+ * struct vdpa_notification_area - vDPA notification area
  * @addr: base address of the notification area
  * @size: size of the notification area
  */
@@ -28,7 +28,7 @@ struct vdpa_notification_area {
 };
 
 /**
- * vDPA vq_state definition
+ * struct vdpa_vq_state - vDPA vq_state definition
  * @avail_index: available index
  */
 struct vdpa_vq_state {
@@ -38,7 +38,7 @@ struct vdpa_vq_state {
 struct vdpa_mgmt_dev;
 
 /**
- * vDPA device - representation of a vDPA device
+ * struct vdpa_device - representation of a vDPA device
  * @dev: underlying device
  * @dma_dev: the actual device that is performing DMA
  * @config: the configuration ops for this device.
@@ -59,7 +59,7 @@ struct vdpa_device {
 };
 
 /**
- * vDPA IOVA range - the IOVA range support by the device
+ * struct vdpa_iova_range - the IOVA range support by the device
  * @first: start of the IOVA range
  * @last: end of the IOVA range
  */
@@ -69,7 +69,7 @@ struct vdpa_iova_range {
 };
 
 /**
- * vDPA_config_ops - operations for configuring a vDPA device.
+ * struct vdpa_config_ops - operations for configuring a vDPA device.
  * Note: vDPA device drivers are required to implement all of the
  * operations unless it is mentioned to be optional in the following
  * list.
@@ -267,7 +267,7 @@ int _vdpa_register_device(struct vdpa_device *vdev, int nvqs);
 void _vdpa_unregister_device(struct vdpa_device *vdev);
 
 /**
- * vdpa_driver - operations for a vDPA driver
+ * struct vdpa_driver - operations for a vDPA driver
  * @driver: underlying device driver
  * @probe: the function to call when a device is found.  Returns 0 or -errno.
  * @remove: the function to call when a device is removed.
@@ -344,7 +344,7 @@ static inline void vdpa_get_config(struct vdpa_device *vdev, unsigned offset,
 }
 
 /**
- * vdpa_mgmtdev_ops - vdpa device ops
+ * struct vdpa_mgmtdev_ops - vdpa device ops
  * @dev_add: Add a vdpa device using alloc and register
  *	     @mdev: parent device to use for device addition
  *	     @name: name of the new vdpa device