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 drivers/vdpa/vdpa.c
drivers/vdpa/vdpa.c:67: info: Scanning doc for __vdpa_alloc_device
drivers/vdpa/vdpa.c:84: warning: No description found for return value of '__vdpa_alloc_device'
drivers/vdpa/vdpa.c:153: info: Scanning doc for _vdpa_register_device
drivers/vdpa/vdpa.c:163: warning: No description found for return value of '_vdpa_register_device'
drivers/vdpa/vdpa.c:172: info: Scanning doc for vdpa_register_device
drivers/vdpa/vdpa.c:180: warning: No description found for return value of 'vdpa_register_device'
drivers/vdpa/vdpa.c:191: info: Scanning doc for _vdpa_unregister_device
drivers/vdpa/vdpa.c:205: info: Scanning doc for vdpa_unregister_device
drivers/vdpa/vdpa.c:217: info: Scanning doc for __vdpa_register_driver
drivers/vdpa/vdpa.c:224: warning: No description found for return value of '__vdpa_register_driver'
drivers/vdpa/vdpa.c:233: info: Scanning doc for vdpa_unregister_driver
drivers/vdpa/vdpa.c:243: info: Scanning doc for vdpa_mgmtdev_register
drivers/vdpa/vdpa.c:250: warning: No description found for return value of 'vdpa_mgmtdev_register'

After the fix:

scripts/kernel-doc -v -none drivers/vdpa/vdpa.c
drivers/vdpa/vdpa.c:67: info: Scanning doc for __vdpa_alloc_device
drivers/vdpa/vdpa.c:153: info: Scanning doc for _vdpa_register_device
drivers/vdpa/vdpa.c:172: info: Scanning doc for vdpa_register_device
drivers/vdpa/vdpa.c:191: info: Scanning doc for _vdpa_unregister_device
drivers/vdpa/vdpa.c:205: info: Scanning doc for vdpa_unregister_device
drivers/vdpa/vdpa.c:217: info: Scanning doc for __vdpa_register_driver
drivers/vdpa/vdpa.c:233: info: Scanning doc for vdpa_unregister_driver
drivers/vdpa/vdpa.c:243: info: Scanning doc for vdpa_mgmtdev_register

[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/20210406170457.98481-3-parav@nvidia.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/vdpa/vdpa.c

@@ -75,7 +75,7 @@ static void vdpa_release_dev(struct device *d)
  * Driver should use vdpa_alloc_device() wrapper macro instead of
  * using this directly.
  *
- * Returns an error when parent/config/dma_dev is not set or fail to get
+ * Return: Returns an error when parent/config/dma_dev is not set or fail to get
  *	   ida.
  */
 struct vdpa_device *__vdpa_alloc_device(struct device *parent,
@@ -157,7 +157,7 @@ static int __vdpa_register_device(struct vdpa_device *vdev, int nvqs)
  * @vdev: the vdpa device to be registered to vDPA bus
  * @nvqs: number of virtqueues supported by this device
  *
- * Returns an error when fail to add device to vDPA bus
+ * Return: Returns an error when fail to add device to vDPA bus
  */
 int _vdpa_register_device(struct vdpa_device *vdev, int nvqs)
 {
@@ -174,7 +174,7 @@ EXPORT_SYMBOL_GPL(_vdpa_register_device);
  * @vdev: the vdpa device to be registered to vDPA bus
  * @nvqs: number of virtqueues supported by this device
  *
- * Returns an error when fail to add to vDPA bus
+ * Return: Returns an error when fail to add to vDPA bus
  */
 int vdpa_register_device(struct vdpa_device *vdev, int nvqs)
 {
@@ -218,7 +218,7 @@ EXPORT_SYMBOL_GPL(vdpa_unregister_device);
  * @drv: the vdpa device driver to be registered
  * @owner: module owner of the driver
  *
- * Returns an err when fail to do the registration
+ * Return: Returns an err when fail to do the registration
  */
 int __vdpa_register_driver(struct vdpa_driver *drv, struct module *owner)
 {
@@ -245,6 +245,8 @@ EXPORT_SYMBOL_GPL(vdpa_unregister_driver);
  * @mdev: Pointer to vdpa management device
  * vdpa_mgmtdev_register() register a vdpa management device which supports
  * vdpa device management.
+ * Return: Returns 0 on success or failure when required callback ops are not
+ *         initialized.
  */
 int vdpa_mgmtdev_register(struct vdpa_mgmt_dev *mdev)
 {