net: dsa: lan9303: correctly check return value of devm_gpiod_get_optional

Function devm_gpiod_get_optional() returns an ERR_PTR on failure. Its
return value should not be validated by a NULL check. Instead, use IS_ERR.
Signed-off-by: Pan Bian <bianpan2016@163.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/lan9303-core.c

@@ -1301,7 +1301,7 @@ static void lan9303_probe_reset_gpio(struct lan9303 *chip,
 	chip->reset_gpio = devm_gpiod_get_optional(chip->dev, "reset",
 						   GPIOD_OUT_LOW);
 
-	if (!chip->reset_gpio) {
+	if (IS_ERR(chip->reset_gpio)) {
 		dev_dbg(chip->dev, "No reset GPIO defined\n");
 		return;
 	}