ALSA: hda/conexant - Enable stereo mix input for CX20549 and CX20551

Both CX20549 and CX20551 codecs have a mixer widget and it can be
connected as the ADC source.  Like AD and VIA codecs, enable the
add_stereo_mix_input flag for these codecs.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/hda/patch_conexant.c

@@ -3424,12 +3424,14 @@ static int patch_conexant_auto(struct hda_codec *codec)
 	case 0x14f15045:
 		codec->single_adc_amp = 1;
 		spec->gen.mixer_nid = 0x17;
+		spec->gen.add_stereo_mix_input = 1;
 		snd_hda_pick_fixup(codec, cxt5045_fixup_models,
 				   cxt5045_fixups, cxt_fixups);
 		break;
 	case 0x14f15047:
 		codec->pin_amp_workaround = 1;
 		spec->gen.mixer_nid = 0x19;
+		spec->gen.add_stereo_mix_input = 1;
 		snd_hda_pick_fixup(codec, cxt5047_fixup_models,
 				   cxt5047_fixups, cxt_fixups);
 		break;