[media] drivers/media/video: fix memory leak of snd_cx18_init()

cxsc is not freed in the error case.

Signed-off-by: Andre Bartke <andre.bartke@gmail.com>
Cc: Andy Walls <awalls@md.metrocast.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>