usb: gadget: udc: mv_udc: do not rely on 'driver' argument

future patches will remove the extra 'driver'
argument to ->udc_stop(), in order to do that,
we must make sure that our UDC does not rely
on it first.

Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/udc/mv_udc_core.c

@@ -1386,7 +1386,7 @@ static int mv_udc_stop(struct usb_gadget *gadget,
 
 	/* stop all usb activities */
 	udc->gadget.speed = USB_SPEED_UNKNOWN;
-	stop_activity(udc, driver);
+	stop_activity(udc, NULL);
 	mv_udc_disable(udc);
 
 	spin_unlock_irqrestore(&udc->lock, flags);