[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>

sound/pci/hda/patch_via.c

@@ -377,6 +377,17 @@ static int via_dig_playback_pcm_close(struct hda_pcm_stream *hinfo,
 	return snd_hda_multi_out_dig_close(codec, &spec->multiout);
 }
 
+static int via_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 via_spec *spec = codec->spec;
+	return snd_hda_multi_out_dig_prepare(codec, &spec->multiout,
+					     stream_tag, format, substream);
+}
+
 /*
  * Analog capture
  */
@@ -433,7 +444,8 @@ static struct hda_pcm_stream vt1708_pcm_digital_playback = {
 	/* NID is set in via_build_pcms */
 	.ops = {
 		.open = via_dig_playback_pcm_open,
-		.close = via_dig_playback_pcm_close
+		.close = via_dig_playback_pcm_close,
+		.prepare = via_dig_playback_pcm_prepare
 	},
 };