V4L/DVB (12167): tuner-xc2028: Fix 7 MHz DVB-T

The following patch should fix 7 MHz DVB-T with the XC3028 using the
DTV7 firmware from the xc3028-v27.fw firmware image.

Tested-by: Terry Wu <terrywu2009@gmail.com>
[mchehab@redhat.com: thanks to John Ferlito, we have a real test in Australia]
Signed-off-by: Andy Walls <awalls@radix.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>