ALSA: hda - Handle pin NID 0x1a on ALC259/269

The pin NID 0x1a should be handled as well as NID 0x1b.
Also added comments.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/hda/patch_realtek.c

@@ -13158,7 +13158,8 @@ static int alc268_new_analog_output(struct alc_spec *spec, hda_nid_t nid,
 		dac = 0x02;
 		break;
 	case 0x15:
-	case 0x1b:
+	case 0x1a: /* ALC259/269 only */
+	case 0x1b: /* ALC259/269 only */
 	case 0x21: /* ALC269vb has this pin, too */
 		dac = 0x03;
 		break;