[media] gspca_sonixb: Fix OV7630 gain control

The ov7630's gain is weird, at 32 the gain drops to the same level as at 16,
so skip 32-47 (of the 0-63 scale).

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>