media: mc: delete redundant code in __media_device_unregister_entity

media_gobj_destroy has already set graph_obj.mdev to NULL. There is no
need to set it again.

[Sakari Ailus: Remove extra newline, rewrap commit msg]

Signed-off-by: Hangyu Hua <[e-mail]>
Reviewed-by: Laurent Pinchart <[e-mail]>
Signed-off-by: Sakari Ailus <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/mc/mc-device.c

···
 	media_gobj_destroy(&entity->graph_obj);
 
 	/* invoke entity_notify callbacks to handle entity removal?? */
-
-	entity->graph_obj.mdev = NULL;
 }
 
 int __must_check media_device_register_entity(struct media_device *mdev,