ALSA: usb-audio: avoid setting of sample rate multiple times on bus

Some of userland applications call 'snd_pcm_hw_params()' and
'snd_pcm_hw_prepare()' sequentially, which means 'snd_pcm_hw_prepare()'
is called twice and the second 'snd_pcm_hw_prepare()' is called in
'SNDRV_PCM_STATE_PREPARED' state.

Some devices are not able to manage this and they will stop playback
if the sample rate will be configured several times over USB protocol.

V2: updated Changelog
Signed-off-by: Daniel Girnus <dgirnus@de.adit-jv.com>
Signed-off-by: Jens Lorenz <jlorenz@de.adit-jv.com>
Signed-off-by: Jiada Wang <jiada_wang@mentor.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/pcm.c

@@ -806,6 +806,8 @@ static int snd_usb_pcm_prepare(struct snd_pcm_substream *substream)
 	if (ret < 0)
 		goto unlock;
 
+	if (subs->need_setup_ep) {
+
 		iface = usb_ifnum_to_if(subs->dev, subs->cur_audiofmt->iface);
 		alts = &iface->altsetting[subs->cur_audiofmt->altset_idx];
 		ret = snd_usb_init_sample_rate(subs->stream->chip,
@@ -816,7 +818,6 @@ static int snd_usb_pcm_prepare(struct snd_pcm_substream *substream)
 		if (ret < 0)
 			goto unlock;
 
-	if (subs->need_setup_ep) {
 		ret = configure_endpoint(subs);
 		if (ret < 0)
 			goto unlock;