V4L/DVB (10337): gspca - common: Simplify the debug macros.

The err, warning and info redefinitions don't need the use of
do {} while.

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