V4L/DVB (10336): gspca - all subdrivers: Return ret instead of -1 in sd_mod_init.

Signed-off-by: Alexey Klimov <klimov.linux@gmail.com>
Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>