vhost/vdpa: use get_config_size callback in vhost_vdpa_config_validate()

Let's use the new 'get_config_size()' callback available instead of
using the 'virtio_id' to get the size of the device config space.
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Link: https://lore.kernel.org/r/20210315163450.254396-10-sgarzare@redhat.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>

drivers/vhost/vdpa.c

@@ -188,13 +188,8 @@ static long vhost_vdpa_set_status(struct vhost_vdpa *v, u8 __user *statusp)
 static int vhost_vdpa_config_validate(struct vhost_vdpa *v,
 				      struct vhost_vdpa_config *c)
 {
-	long size = 0;
-
-	switch (v->virtio_id) {
-	case VIRTIO_ID_NET:
-		size = sizeof(struct virtio_net_config);
-		break;
-	}
+	struct vdpa_device *vdpa = v->vdpa;
+	long size = vdpa->config->get_config_size(vdpa);
 
 	if (c->len == 0)
 		return -EINVAL;