ALSA: usb-audio: Use rwsem for disconnect protection

commit 34f3c89fda4fba9fe689db22253ca8db2f5e6386 upstream.

Replace mutex with rwsem for codec->shutdown protection so that
concurrent accesses are allowed.

Also add the protection to snd_usb_autosuspend() and
snd_usb_autoresume(), too.

Reported-by: Matthieu CASTET <matthieu.castet@parrot.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/sound/usb/usbaudio.h b/sound/usb/usbaudio.h
index 3e2b035..6c805a5 100644
--- a/sound/usb/usbaudio.h
+++ b/sound/usb/usbaudio.h
@@ -36,7 +36,7 @@
 	struct snd_card *card;
 	struct usb_interface *pm_intf;
 	u32 usb_id;
-	struct mutex shutdown_mutex;
+	struct rw_semaphore shutdown_rwsem;
 	unsigned int shutdown:1;
 	unsigned int probing:1;
 	unsigned int autosuspended:1;