ASoC: kirkwood: prevent double streaming

The kirkwood audio subsystem presents 2 PCM's for one source.
Streaming on a second PCM while the first one is active
cuts this last one.
Then, ending the last stream gives a kernel trap in free_irq().
Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/kirkwood/kirkwood-dma.c

@@ -148,10 +148,14 @@ static int kirkwood_dma_open(struct snd_pcm_substream *substream)
 	dram = mv_mbus_dram_info();
 	addr = substream->dma_buffer.addr;
 	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
+		if (priv->substream_play)
+			return -EBUSY;
 		priv->substream_play = substream;
 		kirkwood_dma_conf_mbus_windows(priv->io,
 			KIRKWOOD_PLAYBACK_WIN, addr, dram);
 	} else {
+		if (priv->substream_rec)
+			return -EBUSY;
 		priv->substream_rec = substream;
 		kirkwood_dma_conf_mbus_windows(priv->io,
 			KIRKWOOD_RECORD_WIN, addr, dram);