ALSA: hda - Fix input source elements of secondary ADCs on Realtek

Since alc_auto_create_input_ctls() doesn't set the elements for the
secondary ADCs, "Input Source" elemtns for these also get empty, resulting
in buggy outputs of alsactl like:
	control.14 {
		comment.access 'read write'
		comment.type ENUMERATED
		comment.count 1
		iface MIXER
		name 'Input Source'
		index 1
		value 0
	}

This patch fixes alc_mux_enum_*() (and others) to fall back to the
first entry if the secondary input mux is empty.
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Cc: <stable@kernel.org>

sound/pci/hda/patch_realtek.c

@@ -411,6 +411,8 @@ static int alc_mux_enum_info(struct snd_kcontrol *kcontrol,
 	unsigned int mux_idx = snd_ctl_get_ioffidx(kcontrol, &uinfo->id);
 	if (mux_idx >= spec->num_mux_defs)
 		mux_idx = 0;
+	if (!spec->input_mux[mux_idx].num_items && mux_idx > 0)
+		mux_idx = 0;
 	return snd_hda_input_mux_info(&spec->input_mux[mux_idx], uinfo);
 }
 
@@ -439,6 +441,8 @@ static int alc_mux_enum_put(struct snd_kcontrol *kcontrol,
 
 	mux_idx = adc_idx >= spec->num_mux_defs ? 0 : adc_idx;
 	imux = &spec->input_mux[mux_idx];
+	if (!imux->num_items && mux_idx > 0)
+		imux = &spec->input_mux[0];
 
 	type = get_wcaps_type(get_wcaps(codec, nid));
 	if (type == AC_WID_AUD_MIX) {
@@ -10105,6 +10109,8 @@ static void alc882_auto_init_input_src(struct hda_codec *codec)
 			continue;
 		mux_idx = c >= spec->num_mux_defs ? 0 : c;
 		imux = &spec->input_mux[mux_idx];
+		if (!imux->num_items && mux_idx > 0)
+			imux = &spec->input_mux[0];
 		for (idx = 0; idx < conns; idx++) {
 			/* if the current connection is the selected one,
 			 * unmute it as default - otherwise mute it