usb: gadget: udc-xilinx: clean up a variable name

"ep->udc->lock" and "udc->lock" are the same thing.  It confuses Smatch
if we don't use the same name consistently.
Reviewed-by: NSören Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NFelipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/udc/udc-xilinx.c

@@ -1151,7 +1151,7 @@ static int xudc_ep_dequeue(struct usb_ep *_ep, struct usb_request *_req)
 			break;
 	}
 	if (&req->usb_req != _req) {
-		spin_unlock_irqrestore(&ep->udc->lock, flags);
+		spin_unlock_irqrestore(&udc->lock, flags);
 		return -EINVAL;
 	}
 	xudc_done(ep, req, -ECONNRESET);