usb: dwc3: dwc3_get_extcon() can be static

Fix sparse warning

Fixes: 5f0b74e5 ("USB: dwc3: get extcon device by OF graph bindings")
Reviewed-by: NAndrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Nkbuild test robot <fengguang.wu@intel.com>
Signed-off-by: NFelipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc3/drd.c

@@ -440,7 +440,7 @@ static int dwc3_drd_notifier(struct notifier_block *nb,
 	return NOTIFY_DONE;
 }
 
-struct extcon_dev *dwc3_get_extcon(struct dwc3 *dwc)
+static struct extcon_dev *dwc3_get_extcon(struct dwc3 *dwc)
 {
 	struct device *dev = dwc->dev;
 	struct device_node *np_phy, *np_conn;