V4L/DVB (10984): lgdt3305: avoid OOPS in error path of lgdt3305_attach

Setting state->frontend.demodulator_priv to NULL in the event of
a kzalloc error will result in an OOPS.  Just remove that line.

Thanks to Matthias Schwarzott for pointing this out.

Cc: Matthias Schwarzott <zzam@gentoo.org>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>