[media] au8522: bug-fix: enable modulation AFTER tune (instead of before tuning)

The au8522 driver programs the tuner after programming the demodulator,
but the tuner should be programmed first. This patch fixes this behavior.

EDIT: Apparantly Devin created a similar patch some time ago, but hasn't
submitted it for merge.  I never saw his patch, but I thank him anyhow
for his efforts.  In addition, Devin pointed out a flaw in my patch:

This newly generated patch takes Devin's comments into account.

Thanks-to: Devin Heitmueller <dheitmueller@kernellabs.com>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Cc: stable@kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>