[media] media-entity: only call dev_dbg_obj if mdev is not NULL

Fix kernel Oops NULL pointer deference
Call dev_dbg_obj only after checking if gobj->mdev is not NULL
Signed-off-by: Helen Koike <helen.koike@collabora.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/media-entity.c

@@ -199,12 +199,12 @@ void media_gobj_create(struct media_device *mdev,
 
 void media_gobj_destroy(struct media_gobj *gobj)
 {
-	dev_dbg_obj(__func__, gobj);
-
 	/* Do nothing if the object is not linked. */
 	if (gobj->mdev == NULL)
 		return;
 
+	dev_dbg_obj(__func__, gobj);
+
 	gobj->mdev->topology_version++;
 
 	/* Remove the object from mdev list */