media: staging: media: zoran: drop read/write support

This makes no sense for MJPEG formats and it is just easier to
drop support for this altogether.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>