vdpa: Add missing comment for virtqueue count

Add missing comment for number of virtqueue.
Signed-off-by: Parav Pandit <parav@nvidia.com>
Reviewed-by: Eli Cohen <elic@nvidia.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20201112064005.349268-2-parav@nvidia.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>

include/linux/vdpa.h

@@ -42,6 +42,7 @@ struct vdpa_vq_state {
  * @config: the configuration ops for this device.
  * @index: device index
  * @features_valid: were features initialized? for legacy guests
+ * @nvqs: maximum number of supported virtqueues
  */
 struct vdpa_device {
 	struct device dev;