usb: dwc2: gadget: Check for ep0 in enable

Replaced the WARN_ON with a check and return of -EINVAL in the
dwc2_hsotg_ep_enable function if ep0 is passed in.
Signed-off-by: Vahram Aharonyan <vahrama@synopsys.com>
Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc2/gadget.c

@@ -2631,7 +2631,10 @@ static int dwc2_hsotg_ep_enable(struct usb_ep *ep,
 		desc->wMaxPacketSize, desc->bInterval);
 
 	/* not to be called for EP0 */
-	WARN_ON(index == 0);
+	if (index == 0) {
+		dev_err(hsotg->dev, "%s: called for EP 0\n", __func__);
+		return -EINVAL;
+	}
 
 	dir_in = (desc->bEndpointAddress & USB_ENDPOINT_DIR_MASK) ? 1 : 0;
 	if (dir_in != hs_ep->dir_in) {