[media] gspca - sn9c20x: Change the exposure setting of Omnivision sensors

The exposure of Omnivision sensors is defined by the registers 07, 10 and 04.
This patch updates the registers 10 and 04 before using the registers 2d
and 2e (dummy lines).

Signed-off-by: Jean-François Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>