[media] dvb_usb_v2: get rid of dvb_usb_device state

Remove state from struct dvb_usb_device as we can live without.
Add some debug logs.

Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>