V4L/DVB (5757): Tea5761: store tuning operations in tuner_operations structure

Create static struct tuner_operations tea5761_tuner_ops
for tea5761 tuning function callback pointers

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