clocksource/drivers/ingenic_ost: Fix return value check in ingenic_ost_probe()

In case of error, the function device_node_to_regmap() returns
ERR_PTR() and never returns NULL. The NULL test in the return
value check should be replaced with IS_ERR().

Fixes: ca7b72b5 ("clocksource: Add driver for the Ingenic JZ47xx OST")
Reported-by: NHulk Robot <hulkci@huawei.com>
Signed-off-by: NWei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: NDaniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20210308123031.2285083-1-weiyongjun1@huawei.com

drivers/clocksource/ingenic-ost.c

@@ -88,9 +88,9 @@ static int __init ingenic_ost_probe(struct platform_device *pdev)
 		return PTR_ERR(ost->regs);
 
 	map = device_node_to_regmap(dev->parent->of_node);
-	if (!map) {
+	if (IS_ERR(map)) {
 		dev_err(dev, "regmap not found");
-		return -EINVAL;
+		return PTR_ERR(map);
 	}
 
 	ost->clk = devm_clk_get(dev, "ost");