mailbox: arm_mhuv2: Fix return value check in mhuv2_probe()

If devm_of_iomap() fails, it returns ERR_PTR() and never
return NULL, so replace NULL pointer check with IS_ERR()
to fix this problem.

Fixes: 5a6338cc ("mailbox: arm_mhuv2: Add driver")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>

drivers/mailbox/arm_mhuv2.c

@@ -1062,8 +1062,8 @@ static int mhuv2_probe(struct amba_device *adev, const struct amba_id *id)
 	int ret = -EINVAL;
 
 	reg = devm_of_iomap(dev, dev->of_node, 0, NULL);
-	if (!reg)
-		return -ENOMEM;
+	if (IS_ERR(reg))
+		return PTR_ERR(reg);
 
 	mhu = devm_kzalloc(dev, sizeof(*mhu), GFP_KERNEL);
 	if (!mhu)