[media] mxl5007t: bugfix DVB-T 7 MHz and 8 MHz bandwidth

DVB-T did not work at all - only 6 MHz was working but it is not
commonly used.
Fix it.

Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>