ALSA: Enable SPDIF output on ALC655

Some hardwares with ALC655 codec don't indicate the proper ext id bit
for SPDIF output although it supports.  Force to enable the bit.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/ac97/ac97_patch.c

@@ -2832,6 +2832,8 @@ static int patch_alc655(struct snd_ac97 * ac97)
 			val &= ~(1 << 1); /* Pin 47 is EAPD (for internal speaker) */
 		else
 			val |= (1 << 1); /* Pin 47 is spdif input pin */
+		/* this seems missing on some hardwares */
+		ac97->ext_id |= AC97_EI_SPDIF;
 	}
 	val &= ~(1 << 12); /* vref enable */
 	snd_ac97_write_cache(ac97, 0x7a, val);