[ALSA] hda-codec - Fix SPDIF output

Fix SPDIF output (at least on Realtek codecs).  The DIGI_CONVERT verbs
have to be reset before the PCM stream is set up.  Otherwise the digital
setup is screwed up.
Also, check the AMP capability before setting AMP of the digital out
widget.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>
diff --git a/sound/pci/hda/patch_sigmatel.c b/sound/pci/hda/patch_sigmatel.c
index 6dd4822..612d355 100644
--- a/sound/pci/hda/patch_sigmatel.c
+++ b/sound/pci/hda/patch_sigmatel.c
@@ -814,6 +814,17 @@
 	return snd_hda_multi_out_dig_close(codec, &spec->multiout);
 }
 
+static int stac92xx_dig_playback_pcm_prepare(struct hda_pcm_stream *hinfo,
+					 struct hda_codec *codec,
+					 unsigned int stream_tag,
+					 unsigned int format,
+					 struct snd_pcm_substream *substream)
+{
+	struct sigmatel_spec *spec = codec->spec;
+	return snd_hda_multi_out_dig_prepare(codec, &spec->multiout,
+					     stream_tag, format, substream);
+}
+
 
 /*
  * Analog capture callbacks
@@ -848,7 +859,8 @@
 	/* NID is set in stac92xx_build_pcms */
 	.ops = {
 		.open = stac92xx_dig_playback_pcm_open,
-		.close = stac92xx_dig_playback_pcm_close
+		.close = stac92xx_dig_playback_pcm_close,
+		.prepare = stac92xx_dig_playback_pcm_prepare
 	},
 };