watchdog: at91rm9200: Correct check for syscon_node_to_regmap() errors

syscon_node_to_regmap() returns a regmap or an ERR_PTR().
Signed-off-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

drivers/watchdog/at91rm9200_wdt.c

@@ -244,7 +244,7 @@ static int at91wdt_probe(struct platform_device *pdev)
 	}
 
 	regmap_st = syscon_node_to_regmap(parent->of_node);
-	if (!regmap_st)
+	if (IS_ERR(regmap_st))
 		return -ENODEV;
 
 	res = misc_register(&at91wdt_miscdev);