usb: gadget: clean the ep in autoconf before returning it.

Since commit 72c973dd aka ("usb: gadget: add usb_endpoint_descriptor to
struct usb_ep) the descriptor is part of the ep. Most gadgets like
g_zero or masstorage call config_ep_by_speed() to grab an available
endpoint which may be used for FS/HS/SS bulk/iso/intr and in a second
they assign the proper descriptor by calling config_ep_by_speed(). This
is good so far. A few of them like ncm call config_ep_by_speed() only if
ep->desc not assigned earlier. That means ep->desc is never assigned if
the endpoint was used by another gadget before it was removed.

Some of those gadgets also assign ep->driver_data to NULL on reset or
ep_disable part _but_ keep a reference to this endpoint. At ep_enable
time they assign driver_data to their private data. This probably needs
a clean up of its own.

Signed-off-by: Sebastian Andrzej Siewior <[e-mail]>
Signed-off-by: Felipe Balbi <[e-mail]>

drivers/usb/gadget/epautoconf.c

···
 		/* ep-e, ep-f are PIO with only 64 byte fifos */
 		ep = find_ep (gadget, "ep-e");
 		if (ep && ep_matches(gadget, ep, desc, ep_comp))
-			return ep;
+			goto found_ep;
 		ep = find_ep (gadget, "ep-f");
 		if (ep && ep_matches(gadget, ep, desc, ep_comp))
-			return ep;
+			goto found_ep;
 
 	} else if (gadget_is_goku (gadget)) {
 		if (USB_ENDPOINT_XFER_INT == type) {
 			/* single buffering is enough */
 			ep = find_ep(gadget, "ep3-bulk");
 			if (ep && ep_matches(gadget, ep, desc, ep_comp))
-				return ep;
+				goto found_ep;
 		} else if (USB_ENDPOINT_XFER_BULK == type
 				&& (USB_DIR_IN & desc->bEndpointAddress)) {
 			/* DMA may be available */
 			ep = find_ep(gadget, "ep2-bulk");
 			if (ep && ep_matches(gadget, ep, desc,
 					      ep_comp))
-				return ep;
+				goto found_ep;
 		}
 
 #ifdef CONFIG_BLACKFIN
···
 		} else
 			ep = NULL;
 		if (ep && ep_matches(gadget, ep, desc, ep_comp))
-			return ep;
+			goto found_ep;
 #endif
 	}
 
 	/* Second, look at endpoints until an unclaimed one looks usable */
 	list_for_each_entry (ep, &gadget->ep_list, ep_list) {
 		if (ep_matches(gadget, ep, desc, ep_comp))
-			return ep;
+			goto found_ep;
 	}
 
 	/* Fail */
 	return NULL;
+found_ep:
+	ep->desc = NULL;
+	ep->comp_desc = NULL;
+	return ep;
 }
 
 /**