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 <[e-mail]>
Signed-off-by: Wei Yongjun <[e-mail]>
Signed-off-by: Marc Zyngier <[e-mail]>

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

···
 		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;
 	}