usb: dwc2: gadget: remove of_node reference upon udc_stop

In dwc2_hsotg_udc_start(), e.g. when binding composite driver, "of_node"
is set to hsotg->dev->of_node.

It causes errors when binding the gadget driver several times, on
stm32mp157c-ev1 board. Below error is seen:
"pin PA10 already requested by 49000000.usb-otg; cannot claim for gadget.0"

The first time, no issue is seen as when registering the driver, of_node
isn't NULL:
-> gadget_dev_desc_UDC_store
  -> usb_gadget_register_driver_owner
    -> driver_register
    ...
      -> really_probe -> pinctrl_bind_pins (no effect)

Then dwc2_hsotg_udc_start() sets of_node.

The second time (stop the gadget, reconfigure it, then start it again),
of_node has been set, so the probing code tries to acquire pins for the
gadget. These pins are hold by the controller, hence the error.

So clear gadget.dev.of_node in udc_stop() routine to avoid the issue.

Fixes: 7d7b22928b ("usb: gadget: s3c-hsotg: Propagate devicetree to gadget drivers")
Cc: stable <stable@kernel.org>
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Link: https://lore.kernel.org/r/20250124173325.2747710-1-fabrice.gasnier@foss.st.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/dwc2/gadget.c

@@ -4615,6 +4615,7 @@ static int dwc2_hsotg_udc_stop(struct usb_gadget *gadget)
 	spin_lock_irqsave(&hsotg->lock, flags);
 
 	hsotg->driver = NULL;
+	hsotg->gadget.dev.of_node = NULL;
 	hsotg->gadget.speed = USB_SPEED_UNKNOWN;
 	hsotg->enabled = 0;