ALSA: hda - fix "num_steps = 0" error on ALC256

ALSA: hda - fix "num_steps = 0" error on ALC256

The ALC256 does not have a mixer nid at 0x0b, and there's no
loopback path (the output pins are directly connected to the DACs).

This commit fixes an "num_steps = 0 for NID=0xb (ctl = Beep Playback Volume)"
error (and as a result, problems with amixer/alsamixer).

If there's pcbeep functionality, it certainly isn't controlled by setting an
amp on 0x0b, so disable beep functionality (at least for now).

Cc: stable@vger.kernel.org
BugLink: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1446517
Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>