[media] cx231xx: set standard tune to last known frequency when switching inputs

If switching to a tuner input, reset the standard and tune to the last known
frequency.  We need to do this in particular for this bridge since the tuner
gets powered down when captuing on the composite or s-video inputs.

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