usb: gadget: Clear usb_endpoint_descriptor inside the struct usb_ep on disable

This fix a bug in f_serial, which expect the ep->desc to be NULL after
disabling an endpoint.

Cc: stable@vger.kernel.org
Signed-off-by: Ido Shayevitz <idos@codeaurora.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>
diff --git a/drivers/usb/gadget/pxa25x_udc.c b/drivers/usb/gadget/pxa25x_udc.c
index dd47063..33adf38 100644
--- a/drivers/usb/gadget/pxa25x_udc.c
+++ b/drivers/usb/gadget/pxa25x_udc.c
@@ -283,6 +283,7 @@
 	pxa25x_ep_fifo_flush (_ep);
 
 	ep->desc = NULL;
+	ep->ep.desc = NULL;
 	ep->stopped = 1;
 
 	local_irq_restore(flags);
@@ -1192,6 +1193,7 @@
 			list_add_tail (&ep->ep.ep_list, &dev->gadget.ep_list);
 
 		ep->desc = NULL;
+		ep->ep.desc = NULL;
 		ep->stopped = 0;
 		INIT_LIST_HEAD (&ep->queue);
 		ep->pio_irqs = 0;