udc: net2280: Fix net2280_disable

A reset e.g. calling ep_reset_338x() can happen while endpoints
are enabled. The ep_reset_338x() sets ep->desc = NULL to mark
endpoint being invalid. A subsequent call of net2280_disable will
fail and return -EINVAL to parent function usb_ep_disable(),
which will fail, too, and do not set the member ep->enabled = false.

See:
https://elixir.bootlin.com/linux/v5.0-rc5/source/drivers/usb/gadget/udc/core.c#L139

This fix ignores dp->desc and allows net2280_disable() to succeed.
Subsequent calls to usb_ep_enable()/usb_ep_disable() succeeds.
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Guido Kiener <guido.kiener@rohde-schwarz.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/udc/net2280.c

@@ -516,8 +516,8 @@ static int net2280_disable(struct usb_ep *_ep)
 	unsigned long		flags;
 
 	ep = container_of(_ep, struct net2280_ep, ep);
-	if (!_ep || !ep->desc || _ep->name == ep0name) {
-		pr_err("%s: Invalid ep=%p or ep->desc\n", __func__, _ep);
+	if (!_ep || _ep->name == ep0name) {
+		pr_err("%s: Invalid ep=%p\n", __func__, _ep);
 		return -EINVAL;
 	}
 	spin_lock_irqsave(&ep->dev->lock, flags);