In cases where the device does not actually provide a USB audio class *or*
vendor audio, do not load the driver that provides vendor audio support (such
as the KWorld 2800d).  Otherwise, the /dev/audio1 device file gets created and
users get confused.

Also, reworks the logic a bit so that we don't try to inspect the register
content if the register read failed entirely.
Signed-off-by: NDevin Heitmueller <dheitmueller@kernellabs.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>