The via driver spews warnigs like
	hda-codec: no NID for mapping control Independent HP:0:0
with some codecs because snd_hda_add_nid() is called with nid=0.
This patch fixes it by skipping the call when no corresponding widget
is found.
Signed-off-by: Takashi Iwai <tiwai@suse.de>
        knew->subdevice = HDA_SUBDEV_NID_FLAG | nid;
        knew->private_value = nid;
 
-       knew = via_clone_control(spec, &via_hp_mixer[1]);
-       if (knew == NULL)
-               return -ENOMEM;
-       knew->subdevice = side_mute_channel(spec);
+       nid = side_mute_channel(spec);
+       if (nid) {
+               knew = via_clone_control(spec, &via_hp_mixer[1]);
+               if (knew == NULL)
+                       return -ENOMEM;
+               knew->subdevice = nid;
+       }
 
        return 0;
 }