can: flexcan: fix 'passing zero to ERR_PTR()' warning

Fix a static code checker warning:
drivers/net/can/flexcan.c:1435 flexcan_setup_stop_mode() warn: passing zero to 'PTR_ERR'

Fixes: de3578c1 ("can: flexcan: add self wakeup support")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/flexcan.c

@@ -1432,7 +1432,7 @@ static int flexcan_setup_stop_mode(struct platform_device *pdev)
 	gpr_np = of_find_node_by_phandle(phandle);
 	if (!gpr_np) {
 		dev_dbg(&pdev->dev, "could not find gpr node by phandle\n");
-		return PTR_ERR(gpr_np);
+		return -ENODEV;
 	}
 
 	priv = netdev_priv(dev);