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>

sound/pci/hda/patch_realtek.c

@@ -5664,6 +5664,7 @@ static int patch_alc269(struct hda_codec *codec)
 		break;
 	case 0x10ec0256:
 		spec->codec_variant = ALC269_TYPE_ALC256;
+		spec->gen.mixer_nid = 0; /* ALC256 does not have any loopback mixer path */
 		break;
 	}
 
@@ -5677,8 +5678,8 @@ static int patch_alc269(struct hda_codec *codec)
 	if (err < 0)
 		goto error;
 
-	if (!spec->gen.no_analog && spec->gen.beep_nid)
-		set_beep_amp(spec, 0x0b, 0x04, HDA_INPUT);
+	if (!spec->gen.no_analog && spec->gen.beep_nid && spec->gen.mixer_nid)
+		set_beep_amp(spec, spec->gen.mixer_nid, 0x04, HDA_INPUT);
 
 	codec->patch_ops = alc_patch_ops;
 	codec->patch_ops.stream_pm = snd_hda_gen_stream_pm;