ALSA: usb - disable broken hw volume for Tenx TP6911

While going through Ubuntu bugs, I discovered this patch being
posted and a confirmation that the patch works as expected.

Finding out how the hw volume really works would be preferrable
to just disabling the broken one, but this would be better than
nothing.

Credit: sndfnsdfin (qawsnews)
BugLink: https://bugs.launchpad.net/bugs/559939


Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>