usb: gadget: at91udc: Don't check for ep->ep.desc

Earlier we used to check for ep->ep.desc to figure out if this ep has
already been enabled and if so, abort.
Ido Shayevitz removed the usb_endpoint_descriptor from private udc
structure 5a6506f00 ("usb: gadget: Update at91_udc to use
usb_endpoint_descriptor	inside the struct usb_ep") but did not fix up
the ep_enable condition because _now_ the member is always true and we
can't check if this ep is enabled twice.

Cc: Ido Shayevitz <idos@codeaurora.org>
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

@@ -475,8 +475,7 @@ static int at91_ep_enable(struct usb_ep *_ep,
 	unsigned long	flags;
 
 	if (!_ep || !ep
-			|| !desc || ep->ep.desc
-			|| _ep->name == ep0name
+			|| !desc || _ep->name == ep0name
 			|| desc->bDescriptorType != USB_DT_ENDPOINT
 			|| (maxpacket = usb_endpoint_maxp(desc)) == 0
 			|| maxpacket > ep->maxpacket) {
@@ -530,7 +529,6 @@ ok:
 	tmp |= AT91_UDP_EPEDS;
 	__raw_writel(tmp, ep->creg);
 
-	ep->ep.desc = desc;
 	ep->ep.maxpacket = maxpacket;
 
 	/*