[media] mt9t031: convert to the control framework

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
[g.liakhovetski@gmx.de: simplified pointer arithmetic]
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>