USB: uss720 fixup refcount position

My testprog do a lot of bitbang - after hours i got following warning and my machine lockups:
WARNING: at /build/buildd/linux-2.6.38/lib/kref.c:34
After debugging uss720 driver i discovered that the completion callback was called before
usb_submit_urb returns. The callback frees the request structure that is krefed on return by
usb_submit_urb.

Signed-off-by: Peter Holik <peter@holik.at>
Acked-by: Thomas Sailer <t.sailer@alumni.ethz.ch>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/misc/uss720.c

@@ -177,12 +177,11 @@ static struct uss720_async_request *submit_async_request(struct parport_uss720_p
 	spin_lock_irqsave(&priv->asynclock, flags);
 	list_add_tail(&rq->asynclist, &priv->asynclist);
 	spin_unlock_irqrestore(&priv->asynclock, flags);
+	kref_get(&rq->ref_count);
 	ret = usb_submit_urb(rq->urb, mem_flags);
-	if (!ret) {
-		kref_get(&rq->ref_count);
+	if (!ret)
 		return rq;
-	}
-	kref_put(&rq->ref_count, destroy_async);
+	destroy_async(&rq->ref_count);
 	err("submit_async_request submit_urb failed with %d", ret);
 	return NULL;
 }