V4L/DVB (6920): tuner: fix backwards logic in check for set_config

tuner-core was checking if analog_ops->set_config is set.  If set, it would
complain that it isn't.  Fix this backwards logic to the proper behavior.

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