uhci: cancel on schedule stop.

Cancel any in-flight transaction when the guest stops the uhci schedule.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

hw/usb/hcd-uhci.c

@@ -1126,6 +1126,7 @@ static void uhci_frame_timer(void *opaque)
     if (!(s->cmd & UHCI_CMD_RS)) {
         /* Full stop */
         qemu_del_timer(s->frame_timer);
+        uhci_async_cancel_all(s);
         /* set hchalted bit in status - UHCI11D 2.1.2 */
         s->status |= UHCI_STS_HCHALTED;