regulator: vexpress: Use PTR_ERR_OR_ZERO() to simplify code

Fixes coccicheck warning:

drivers/regulator/vexpress-regulator.c:78:1-3: WARNING: PTR_ERR_OR_ZERO can be used
Reported-by: NHulk Robot <hulkci@huawei.com>
Signed-off-by: Nzhengbin <zhengbin13@huawei.com>
Link: https://lore.kernel.org/r/1574074762-34629-1-git-send-email-zhengbin13@huawei.comSigned-off-by: NMark Brown <broonie@kernel.org>

drivers/regulator/vexpress-regulator.c

@@ -75,10 +75,7 @@ static int vexpress_regulator_probe(struct platform_device *pdev)
 	config.of_node = pdev->dev.of_node;
 
 	rdev = devm_regulator_register(&pdev->dev, desc, &config);
-	if (IS_ERR(rdev))
-		return PTR_ERR(rdev);
-
-	return 0;
+	return PTR_ERR_OR_ZERO(rdev);
 }
 
 static const struct of_device_id vexpress_regulator_of_match[] = {