usb: gadget: udc: max3420_udc: remove using list iterator after loop body as a ptr

If the list does not contain the expected element, the value of
list_for_each_entry() iterator will not point to a valid structure.
To avoid type confusion in such case, the list iterator
scope will be limited to list_for_each_entry() loop.

In preparation to limiting scope of a list iterator to the list traversal
loop, use a dedicated pointer to point to the found element [1].
Determining if an element was found is then simply checking if
the pointer is != NULL instead of using the potentially bogus pointer.

Link: https://lore.kernel.org/all/YhdfEIwI4EdtHdym@kroah.com/
Signed-off-by: Jakob Koschel <jakobkoschel@gmail.com>
Link: https://lore.kernel.org/r/20220308171818.384491-20-jakobkoschel@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/udc/max3420_udc.c

@@ -1044,22 +1044,26 @@ static int max3420_ep_queue(struct usb_ep *_ep, struct usb_request *_req,
 
 static int max3420_ep_dequeue(struct usb_ep *_ep, struct usb_request *_req)
 {
-	struct max3420_req *t, *req = to_max3420_req(_req);
+	struct max3420_req *t = NULL;
+	struct max3420_req *req = to_max3420_req(_req);
+	struct max3420_req *iter;
 	struct max3420_ep *ep = to_max3420_ep(_ep);
 	unsigned long flags;
 
 	spin_lock_irqsave(&ep->lock, flags);
 
 	/* Pluck the descriptor from queue */
-	list_for_each_entry(t, &ep->queue, queue)
-		if (t == req) {
-			list_del_init(&req->queue);
-			break;
-		}
+	list_for_each_entry(iter, &ep->queue, queue) {
+		if (iter != req)
+			continue;
+		list_del_init(&req->queue);
+		t = iter;
+		break;
+	}
 
 	spin_unlock_irqrestore(&ep->lock, flags);
 
-	if (t == req)
+	if (t)
 		max3420_req_done(req, -ECONNRESET);
 
 	return 0;