usb: dwc2: host: ensure qtb exists before dereferencing it

dwc2_hc_nak_intr could be called with a NULL qtd.
Ensure qtd exists before dereferencing it to avoid kernel panic.
This happens when using usb to ethernet adapter.
Acked-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Gregory Herrero <gregory.herrero@intel.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/dwc2/hcd_intr.c

@@ -1208,6 +1208,16 @@ static void dwc2_hc_nak_intr(struct dwc2_hsotg *hsotg,
 			     struct dwc2_host_chan *chan, int chnum,
 			     struct dwc2_qtd *qtd)
 {
+	if (!qtd) {
+		dev_dbg(hsotg->dev, "%s: qtd is NULL\n", __func__);
+		return;
+	}
+
+	if (!qtd->urb) {
+		dev_dbg(hsotg->dev, "%s: qtd->urb is NULL\n", __func__);
+		return;
+	}
+
 	if (dbg_hc(chan))
 		dev_vdbg(hsotg->dev, "--Host Channel %d Interrupt: NAK Received--\n",
 			 chnum);