irqchip/aspeed-i2c-ic: Fix return value check in aspeed_i2c_ic_of_init()

In case of error, the function of_iomap() returns NULL pointer not
ERR_PTR(). The IS_ERR() test in the return value check should be
replaced with NULL test..
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

drivers/irqchip/irq-aspeed-i2c-ic.c

@@ -76,8 +76,8 @@ static int __init aspeed_i2c_ic_of_init(struct device_node *node,
 		return -ENOMEM;
 
 	i2c_ic->base = of_iomap(node, 0);
-	if (IS_ERR(i2c_ic->base)) {
-		ret = PTR_ERR(i2c_ic->base);
+	if (!i2c_ic->base) {
+		ret = -ENOMEM;
 		goto err_free_ic;
 	}