usb: dwc3: prevent setting PRTCAP to OTG from debugfs

We don't support PRTCAP == OTG yet, so prevent user from
setting it via debugfs.

Fixes: 41ce1456e1db ("usb: dwc3: core: make dwc3_set_mode() work properly")
Cc: <stable@vger.kernel.org> # v4.12+
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc3/core.c

@@ -119,6 +119,9 @@ static void __dwc3_set_mode(struct work_struct *work)
 	if (dwc->dr_mode != USB_DR_MODE_OTG)
 		return;
 
+	if (dwc->desired_dr_role == DWC3_GCTL_PRTCAP_OTG)
+		return;
+
 	switch (dwc->current_dr_role) {
 	case DWC3_GCTL_PRTCAP_HOST:
 		dwc3_host_exit(dwc);