[media] video: sn9c102: world-wirtable sysfs files

Don't allow everybody to change video settings.

Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>
Acked-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Acked-by: Luca Risolia <luca.risolia@studio.unibo.it>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>