usb: gadget: at91udc: don't overwrite driver data

The driver was converted to the new start/stop interface in f3d8bf34
("usb: gadget: at91_udc: convert to new style start/stop interface").
I overlooked that the driver is overwritting the private data which is
used by the composite framework. The udc driver doesn't read it, it is
only written here.
Tested-by: Fabio Porcedda <fabio.porcedda@gmail.com>
Tested-by: Mario Isidoro <Mario.Isidoro@tecmic.pt>
Cc: <stable@kernel.org> # v3.5
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/at91_udc.c

@@ -1635,7 +1635,6 @@ static int at91_start(struct usb_gadget *gadget,
 	udc->driver = driver;
 	udc->gadget.dev.driver = &driver->driver;
 	udc->gadget.dev.of_node = udc->pdev->dev.of_node;
-	dev_set_drvdata(&udc->gadget.dev, &driver->driver);
 	udc->enabled = 1;
 	udc->selfpowered = 1;
 
@@ -1656,7 +1655,6 @@ static int at91_stop(struct usb_gadget *gadget,
 	spin_unlock_irqrestore(&udc->lock, flags);
 
 	udc->gadget.dev.driver = NULL;
-	dev_set_drvdata(&udc->gadget.dev, NULL);
 	udc->driver = NULL;
 
 	DBG("unbound from %s\n", driver->driver.name);