reset: rzg2l-usbphy-ctrl: Fix a NULL vs IS_ERR() bug in probe

The devm_regmap_field_alloc() function never returns NULL, it returns
error pointers.  Update the error checking to match.

Fixes: 58128aa ("reset: rzg2l-usbphy-ctrl: Add support for USB PWRRDY")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

Author: Dan Carpenter

drivers/reset/reset-rzg2l-usbphy-ctrl.c

@@ -158,8 +158,8 @@ static int rzg2l_usbphy_ctrl_pwrrdy_init(struct device *dev)
 	field.msb = __fls(args[1]);
 
 	pwrrdy = devm_regmap_field_alloc(dev, regmap, field);
-	if (!pwrrdy)
-		return -ENOMEM;
+	if (IS_ERR(pwrrdy))
+		return PTR_ERR(pwrrdy);
 
 	rzg2l_usbphy_ctrl_set_pwrrdy(pwrrdy, true);