V4L/DVB (4991): Cafe_ccic.c: fix NULL dereference

We shouldn't dereference "cam" when we already know it's NULL.
Spotted by the Coverity checker.

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>