[ALSA] Fix substream to check in PCM drain

The check of a substream in snd_pcm_drain() might not be always correct
since runtime can point a different substream (although the PCM state
of each linked substream should be same, in theory).
This patch fixes it.
Signed-off-by: NTakashi Iwai <tiwai@suse.de>
Signed-off-by: NJaroslav Kysela <perex@suse.cz>

sound/core/pcm_native.c

@@ -1487,7 +1487,7 @@ static int snd_pcm_drain(struct snd_pcm_substream *substream)
 
 	snd_pcm_stream_lock_irq(substream);
 	/* resume pause */
-	if (runtime->status->state == SNDRV_PCM_STATE_PAUSED)
+	if (substream->runtime->status->state == SNDRV_PCM_STATE_PAUSED)
 		snd_pcm_pause(substream, 0);
 
 	/* pre-start/stop - all running streams are changed to DRAINING state */