V4L/DVB: gspca - ov534: Fix Auto White Balance control

Set only the needed bits for AWB, and enable it by default.

Signed-off-by: Max Thrun <bear24rw@gmail.com>
Signed-off-by: Antonio Ospite <ospite@studenti.unina.it>
Signed-off-by: Jean-François Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>