[media] cx231xx: set correct i2c port for Exeter tuner

The tuner is on i2c port 3 just like all the reference designs.  Having it
improperly set to port #1 causes the tuner initialization to fail when enabling
the device.

Signed-off-by: Devin Heitmueller <dheitmueller@hauppauge.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>