ALSA: hda - Fix initialization of secondary capture source on VT1705

VT1705 codec has two ADCs where the secondary ADC has no MUX but only
a fixed connection to the mic pin.  This confused the driver and it
tries always overriding the input-source selection by assumption of
the existing MUX for the secondary ADC, resulted in resetting the
input-source at each time PM (including power-saving) occurs.

The fix is simply to check the existence of MUX for secondary ADCs in
the initialization code.

Tested-by: Anisse Astier <anisse@astier.eu>
Cc: <stable@kernel.org> [v3.1+]
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/hda/patch_via.c

@@ -666,6 +666,9 @@ static void via_auto_init_analog_input(struct hda_codec *codec)
 	/* init input-src */
 	for (i = 0; i < spec->num_adc_nids; i++) {
 		int adc_idx = spec->inputs[spec->cur_mux[i]].adc_idx;
+		/* secondary ADCs must have the unique MUX */
+		if (i > 0 && !spec->mux_nids[i])
+			break;
 		if (spec->mux_nids[adc_idx]) {
 			int mux_idx = spec->inputs[spec->cur_mux[i]].mux_idx;
 			snd_hda_codec_write(codec, spec->mux_nids[adc_idx], 0,