[media] dvb_usb_v2: .read_mac_address() callback changes

Give DVB adapter as a parameter for callback. MAC address is
adapter property and it could be (at least in theory) there
is devices having multiple adapters and all has own MAC.

Also add error handling. If callback fails error is returned
which leads device unregister.

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