[media] media: drivers shouldn't touch debug field in video_device

The debug field in struct video_device is for internal use only and
drivers should mix that with their own debug module options.

It is handled by the V4L2 core and users can set it using
/sys/class/video4linux/<devX>/debug.

It has been deprecated for some time now, so it is time to remove it
completely from the drivers.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>