V4L/DVB (11461): gspca - m5602-po1030: Probe read only register at probe time

Currently, we're probing r/w registers at probe time.
This is potentially dangerous, probe some read only registers instead.

Signed-off-by: Erik Andr?n <erik.andren@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>