[media] V4L: Remove all links of the media entity when unregistering subdev

Remove all links of the subdev's media entity after internal_ops
'unregistered' call and right before unregistering the entity from
a media device.
It is assumed here that an unregistered (orphan) media entity cannot
have links to other entities registered to a media device.
It is also assumed the media links should be created/removed with
the media graph's mutex held.
The above implies that the caller of v4l2_device_unregister_subdev()
must not hold the graph's mutex.

Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Sakari Ailus <sakari.ailus@iki.fi>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/v4l2-core/v4l2-device.c

@@ -269,8 +269,10 @@ void v4l2_device_unregister_subdev(struct v4l2_subdev *sd)
 	sd->v4l2_dev = NULL;
 
 #if defined(CONFIG_MEDIA_CONTROLLER)
-	if (v4l2_dev->mdev)
+	if (v4l2_dev->mdev) {
+		media_entity_remove_links(&sd->entity);
 		media_device_unregister_entity(&sd->entity);
+	}
 #endif
 	video_unregister_device(sd->devnode);
 	module_put(sd->owner);