V4L/DVB: ngene: properly support boards where channel 0 isn't a TS input

The current code assumes that channel zero is always a TS input, which would
result in an oops if the "one_adapter" modprobe option is 1 (which it is by
default) and the board in question has something else on channel zero (which
is the case for the Avermedia m780, which has it's analog input wired to UVI1)

The code now explicitly tracks the first adapter created and ensures that
other channels cannot accidentially be associated with a NULL adapter.

Also, eliminate what appears to be a typo where all of the channel parameters
are getting associated with stream zero's properties, which will work if you
happen to have a dual stream board with the exact same configuration, but if
they differ then the second stream is going to end up with the first stream's
configuration.

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