[media] tuners/xc5000: fix MODE_AIR in xc5000_set_params()

There is a missing break so we use XC_RF_MODE_CABLE instead of
XC_RF_MODE_AIR.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>