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>
diff --git a/sound/pci/ac97/ac97_patch.c b/sound/pci/ac97/ac97_patch.c
index 6e831af..2c7cd97 100644
--- a/sound/pci/ac97/ac97_patch.c
+++ b/sound/pci/ac97/ac97_patch.c
@@ -2832,6 +2832,8 @@
 			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);