usb: gadget: dummy_hcd: signedness bug in transfer()

"len" is unsigned so it's never less than zero.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/dummy_hcd.c

@@ -1352,7 +1352,7 @@ static int transfer(struct dummy_hcd *dum_hcd, struct urb *urb,
 			len = dummy_perform_transfer(urb, req, len);
 
 			ep->last_io = jiffies;
-			if (len < 0) {
+			if ((int)len < 0) {
 				req->req.status = len;
 			} else {
 				limit -= len;