mfd: hi6421-pmic: Update dev_err messages

Update dev_err messages to make them more readable.

Signed-off-by: Guodong Xu <[e-mail]>
Acked-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>

drivers/mfd/hi6421-pmic-core.c

···
 	pmic->regmap = devm_regmap_init_mmio_clk(&pdev->dev, NULL, base,
 						 &hi6421_regmap_config);
 	if (IS_ERR(pmic->regmap)) {
-		dev_err(&pdev->dev,
-			"regmap init failed: %ld\n", PTR_ERR(pmic->regmap));
+		dev_err(&pdev->dev, "Failed to initialise Regmap: %ld\n",
+						PTR_ERR(pmic->regmap));
 		return PTR_ERR(pmic->regmap);
 	}
 
···
 	ret = devm_mfd_add_devices(&pdev->dev, 0, hi6421_devs,
 				   ARRAY_SIZE(hi6421_devs), NULL, 0, NULL);
 	if (ret) {
-		dev_err(&pdev->dev, "add mfd devices failed: %d\n", ret);
+		dev_err(&pdev->dev, "Failed to add child devices: %d\n", ret);
 		return ret;
 	}