usb: gadget: udc: at91: 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/at91_udc.c

@@ -1657,9 +1657,9 @@ static int at91_stop(struct usb_gadget *gadget,
 	at91_udp_write(udc, AT91_UDP_IDR, ~0);
 	spin_unlock_irqrestore(&udc->lock, flags);
 
+	DBG("unbound from %s\n", udc->driver->driver.name);
 	udc->driver = NULL;
 
-	DBG("unbound from %s\n", driver->driver.name);
 	return 0;
 }