V4L/DVB: gspca_sonixb: pas202: fixup brightness ctrl and add gain and exposure ctrls

Fixup brightness ctrl and add gain and exposure ctrls for PAS202BCB sensors,
this allows enabling autogain (done), and makes the cam usable in low light
conditions.

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