V4L/DVB: tuner-xc2028: fix tuning logic to solve a regression in Australia

There's one reported regression in Australia (DTV7) and some
reported troubles with newer firmwares found on xc3028l chips.
Rework the logic to improve tuner on those cases.

Thanks-to: Robert Lowery <rglowery@exemail.com.au>
Thanks-to: Stefan Ringel <stefan.ringel@arcor.de>
Tested-by: Robert Lowery <rglowery@exemail.com.au>
CC: stable.kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>