V4L/DVB (8887): gspca: fix memory leak

Free allocated memory

Cc: Jean-Francois Moine <moinejf@free.fr>
Cc: Hans de Goede <j.w.r.degoede@hhs.nl>
Signed-off-by: Douglas Schilling Landgraf <dougsland@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>