V4L/DVB (10335): gspca - all subdrivers: Fix CodingStyle in sd_mod_init function.

Introduce int ret and check it value after call to usb_register().

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>