usb: chipidea: udc: zero-length packet is only needed for TX

The zero-length packet is the sendor tells the receiver that there
is no more data, so it is only needed at the TX side.
Signed-off-by: NPeter Chen <peter.chen@freescale.com>

drivers/usb/chipidea/udc.c

@@ -445,7 +445,7 @@ static int _hardware_enqueue(struct ci_hw_ep *hwep, struct ci_hw_req *hwreq)
 		rest -= count;
 	}
 
-	if (hwreq->req.zero && hwreq->req.length
+	if (hwreq->req.zero && hwreq->req.length && hwep->dir == TX
 	    && (hwreq->req.length % hwep->ep.maxpacket == 0))
 		add_td_to_list(hwep, hwreq, 0);