[media] media: use entity.graph_obj.mdev instead of .parent
The struct media_entity has a .parent field that stores a pointer
to the parent struct media_device. But recently a media_gobj was
embedded into the entities and since struct media_gojb already has
a pointer to a struct media_device in the .mdev field, the .parent
field becomes redundant and can be removed.
This patch replaces all the usage of .parent by .graph_obj.mdev so
that field will become unused and can be removed on a later patch.
No functional changes.
The transformation was made using the following coccinelle spatch: