[media] rc_core: avoid kernel oops when rmmod saa7134

The following is a patch to avoid a kernel oops when running rmmod
saa7134 on kernel 2.6.27.1. The change is as suggested by mchehab on
irc.freenode.org

Signed-off-by: Hussam Al-Tayeb <ht990332@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>