V4L/DVB (4847): Drivers/media/dvb/frontends: kfree() cleanups

We don't have to check for NULL before kfree()
Acked-by: Andrew de Quincey <adq_dvb@lidskialf.net>

Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>