usb: dwc3: gadget: don't send extra ZLP

If the request->length is zero, a ZLP should already be sent due to that
and another ZLP is not needed to terminate the transfer.

Fixes: 04c03d10 ("usb: dwc3: gadget: handle request->zero")
Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/dwc3/gadget.c

@@ -1203,7 +1203,8 @@ static int dwc3_gadget_ep_queue(struct usb_ep *ep, struct usb_request *request,
 	 * extra usb_request ourselves so that it gets handled the same way as
 	 * any other request.
 	 */
-	if (ret == 0 && request->zero && (request->length % ep->maxpacket == 0))
+	if (ret == 0 && request->zero && request->length &&
+	    (request->length % ep->maxpacket == 0))
 		ret = __dwc3_gadget_ep_queue_zlp(dwc, dep);
 
 	spin_unlock_irqrestore(&dwc->lock, flags);