ALSA: pcm - Remove BKL from async callback

It's simply calling fasync_helper().
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/pcm_native.c

@@ -3303,18 +3303,13 @@ static int snd_pcm_fasync(int fd, struct file * file, int on)
 	struct snd_pcm_file * pcm_file;
 	struct snd_pcm_substream *substream;
 	struct snd_pcm_runtime *runtime;
-	int err = -ENXIO;
 
-	lock_kernel();
 	pcm_file = file->private_data;
 	substream = pcm_file->substream;
 	if (PCM_RUNTIME_CHECK(substream))
-		goto out;
+		return -ENXIO;
 	runtime = substream->runtime;
-	err = fasync_helper(fd, file, on, &runtime->fasync);
-out:
-	unlock_kernel();
-	return err;
+	return fasync_helper(fd, file, on, &runtime->fasync);
 }
 
 /*