V4L/DVB (8044): au8522: tuning optimizations

If the current modulation and frequency is already set to
the desired parameters, then don't re-tune.

Don't store current frequency until after we've tuned successfully.

Force a re-tune after resume from standby.

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