media: v4l2-dev: Make macros to obtain containers const-aware

Retain the constness of the object in media_entity_to_video_device() and
to_video_device(), by switching to container_of_const().

Signed-off-by: Sakari Ailus <[e-mail]>
Signed-off-by: Hans Verkuil <[e-mail]>

include/media/v4l2-dev.h

···
 	typeof(__entity) __me_vdev_ent = __entity;			\
 									\
 	__me_vdev_ent ?							\
-		container_of(__me_vdev_ent,  struct video_device, entity) : \
-		NULL;							\
+		container_of_const(__me_vdev_ent,  struct video_device, \
+				   entity) : NULL;			\
 })
 
 /**
···
  *
  * @cd: pointer to &struct device
  */
-#define to_video_device(cd) container_of(cd, struct video_device, dev)
+#define to_video_device(cd) container_of_const(cd, struct video_device, dev)
 
 /**
  * __video_register_device - register video4linux devices