V4L/DVB (12518): ov772x: S_CROP must return actually configured geometry

V4L2 drivers are allowed to configure a geometry different than what has been
requested by the user with S_CROP, but then they have to adjust the input
rectangle accordingly. Fix ov772x to comply with this requirement.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>