[media] gspca: Unset debug by default

The output of possible hardware or software errors does not depend on the
option GSPCA_DEBUG. This one is useful only when working on the main driver
or on a subdriver (bug fix, enhancement, new webcam/bridge/sensor or bug fix).
It is enabled in the gspca test version which is available from my web site.

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