ALSA: usb-audio: void return type of snd_usb_endpoint_deactivate()

The return value of snd_usb_endpoint_deactivate() is not used,
make the function have no return value.
Update the documentation to reflect what the function is actually
doing.

Signed-off-by: Eldad Zack <eldad@fogrefinery.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/usb/endpoint.h b/sound/usb/endpoint.h
index 3bd02f0..1c7e8ee 100644
--- a/sound/usb/endpoint.h
+++ b/sound/usb/endpoint.h
@@ -22,7 +22,7 @@
 void snd_usb_endpoint_stop(struct snd_usb_endpoint *ep);
 void snd_usb_endpoint_sync_pending_stop(struct snd_usb_endpoint *ep);
 int  snd_usb_endpoint_activate(struct snd_usb_endpoint *ep);
-int  snd_usb_endpoint_deactivate(struct snd_usb_endpoint *ep);
+void snd_usb_endpoint_deactivate(struct snd_usb_endpoint *ep);
 void snd_usb_endpoint_free(struct list_head *head);
 
 int snd_usb_endpoint_implicit_feedback_sink(struct snd_usb_endpoint *ep);