media: mc: Get media_device directly from pad

Various functions access the media_device from a pad by going through
the entity the pad belongs to. Remove the level of indirection and get
the media_device from the pad directly.

Fixes: 9e3576a1 ("media: mc: convert pipeline funcs to take media_pad")
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-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>