usb: renesas_usbhs: gadget: Fix NULL pointer dereference in usbhsg_ep_dequeue()

This patch fixes an issue that NULL pointer dereference happens when
a gadget driver calls usb_ep_dequeue() for ep0 after disconnected
a usb cable. This is because that usbhsg_try_stop() will call
usbhsg_ep_disable(&dcp->ep) when a usb cable is disconnected and
the pipe of dcp (ep0) is set to NULL.
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/renesas_usbhs/mod_gadget.c

@@ -131,7 +131,8 @@ static void __usbhsg_queue_pop(struct usbhsg_uep *uep,
 	struct device *dev = usbhsg_gpriv_to_dev(gpriv);
 	struct usbhs_priv *priv = usbhsg_gpriv_to_priv(gpriv);
 
-	dev_dbg(dev, "pipe %d : queue pop\n", usbhs_pipe_number(pipe));
+	if (pipe)
+		dev_dbg(dev, "pipe %d : queue pop\n", usbhs_pipe_number(pipe));
 
 	ureq->req.status = status;
 	spin_unlock(usbhs_priv_to_lock(priv));
@@ -685,7 +686,13 @@ static int usbhsg_ep_dequeue(struct usb_ep *ep, struct usb_request *req)
 	struct usbhsg_request *ureq = usbhsg_req_to_ureq(req);
 	struct usbhs_pipe *pipe = usbhsg_uep_to_pipe(uep);
 
-	usbhs_pkt_pop(pipe, usbhsg_ureq_to_pkt(ureq));
+	if (pipe)
+		usbhs_pkt_pop(pipe, usbhsg_ureq_to_pkt(ureq));
+
+	/*
+	 * To dequeue a request, this driver should call the usbhsg_queue_pop()
+	 * even if the pipe is NULL.
+	 */
 	usbhsg_queue_pop(uep, ureq, -ECONNRESET);
 
 	return 0;