[media] usbvision: remove broken testpattern

Enabling force_testpattern module parameter in usbvision causes kernel panic.
Things like that does not belong to the kernel anyway so the fix is easy.

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>