[media] cxd2820r: check bandwidth earlier for DVB-T/T2

It is param that could be potentially unsupported and
due to that it is good idea to check it very first.

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