V4L/DVB: gspca - vc032x: Force main register write at probe time (poxxxx)

On laptops, the webcam sometimes disconnects when writing the first main
register (b300). This patch prevents the creation of a new /dev/video<n>
on streaming start.

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