V4L/DVB (5759): Tuner-simple: store tuning operations in tuner_operations struct

Create static struct tuner_operations simple_tuner_ops
for tuner-simple tuning function callback pointers

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