media: mc: Remove redundant documentation

Remove redundant kerneldoc documentation in mc-device.c. The functions are
already documented in media-device.h, where non-redundant documentation is
also moved.

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