[ALSA] Fix Oops of PCM OSS emulation

Modules: PCM Midlevel,ALSA<-OSS emulation

Fix Oops of PCM OSS emulation occuring when multiple playback is used.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/include/sound/pcm.h b/include/sound/pcm.h
index 66b1f08..e9ab455 100644
--- a/include/sound/pcm.h
+++ b/include/sound/pcm.h
@@ -367,7 +367,7 @@
 	struct snd_pcm_group self_group;	/* fake group for non linked substream (with substream lock inside) */
 	struct snd_pcm_group *group;		/* pointer to current group */
 	/* -- assigned files -- */
-	struct snd_pcm_file *file;
+	void *file;
 	struct file *ffile;
 	void (*pcm_release)(struct snd_pcm_substream *);
 #if defined(CONFIG_SND_PCM_OSS) || defined(CONFIG_SND_PCM_OSS_MODULE)