V4L/DVB (12120): pvrusb2: Change initial default frequency setting

Change default frequency to be US Broadcast channel 3 - with the
transition to d igital the previous value has now become useless.
This change is PURELY to help with my testing (I need to set some kind
of default so it might as well be some thing usable).

Signed-off-by: Mike Isely <isely@pobox.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>