irqchip/exiu: Fix return value check in exiu_init()

In case of error, the function of_iomap() returns NULL pointer not
ERR_PTR().

Replace the IS_ERR() test of the return value with NULL test and return
a proper error code.

Fixes: 706cffc1b912 ("irqchip/exiu: Add support for Socionext Synquacer EXIU controller")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Jason Cooper <jason@lakedaemon.net>
Link: https://lkml.kernel.org/r/1510642648-123574-1-git-send-email-weiyongjun1@huawei.com

drivers/irqchip/irq-sni-exiu.c

@@ -196,8 +196,8 @@ static int __init exiu_init(struct device_node *node,
 	}
 
 	data->base = of_iomap(node, 0);
-	if (IS_ERR(data->base)) {
-		err = PTR_ERR(data->base);
+	if (!data->base) {
+		err = -ENODEV;
 		goto out_free;
 	}