media: mc: entity: Merge media_entity_enum_init and __media_entity_enum_init

The media_entity_enum_init() function is a wrapper around
__media_entity_enum_init() that turns a media_device pointer argument
into the maximum entity ID in the corresponding media graph.
__media_entity_enum_init() is never used outside of
media_entity_enum_init(), so the two functions can be merged together.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>