rtc: 88pm860x: fix possible race condition

The RTC IRQ is requested before the struct rtc_device is allocated,
this may lead to a NULL pointer dereference in the IRQ handler.

To fix this issue, allocating the rtc_device struct before requesting
the RTC IRQ using devm_rtc_allocate_device, and use rtc_register_device
to register the RTC device.

Also remove the unnecessary error message as the core already prints the
info.

Link: https://lore.kernel.org/r/20200311223956.51352-1-alexandre.belloni@bootlin.comSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-88pm860x.c

@@ -336,6 +336,10 @@ static int pm860x_rtc_probe(struct platform_device *pdev)
 	info->dev = &pdev->dev;
 	dev_set_drvdata(&pdev->dev, info);
 
+	info->rtc_dev = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(info->rtc_dev))
+		return PTR_ERR(info->rtc_dev);
+
 	ret = devm_request_threaded_irq(&pdev->dev, info->irq, NULL,
 					rtc_update_handler, IRQF_ONESHOT, "rtc",
 					info);
@@ -377,13 +381,11 @@ static int pm860x_rtc_probe(struct platform_device *pdev)
 		}
 	}
 
-	info->rtc_dev = devm_rtc_device_register(&pdev->dev, "88pm860x-rtc",
-					    &pm860x_rtc_ops, THIS_MODULE);
-	ret = PTR_ERR(info->rtc_dev);
-	if (IS_ERR(info->rtc_dev)) {
-		dev_err(&pdev->dev, "Failed to register RTC device: %d\n", ret);
+	info->rtc_dev->ops = &pm860x_rtc_ops;
+
+	ret = rtc_register_device(info->rtc_dev);
+	if (ret)
 		return ret;
-	}
 
 	/*
 	 * enable internal XO instead of internal 3.25MHz clock since it can