[media] cx24117: remove dead code in always 'false' if statement

At this point of the execution in the function cx24117_attach()
demod cannot be '0'. In that case the function returns earlier
with an error value ('NULL'). Remove the if statement.

This error has been reported by scan.coverity.com

Signed-off-by: Andi Shyti <andi@etezian.org>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>