rtc: rp5c01: Initialize drvdata before registering device

Commit f44f7f96a20 ("RTC: Initialize kernel state from RTC") uncovered
an issue in a number of RTC drivers, where the drivers call
rtc_device_register before initializing the device or platform drvdata.

This frequently results in null pointer dereferences when the
rtc_device_register immediately makes use of the rtc device, calling
rtc_read_alarm.

The solution is to ensure the drvdata is initialized prior to registering
the rtc device.

CC: Wolfram Sang <w.sang@pengutronix.de>
CC: Alessandro Zummo <a.zummo@towertech.it>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: rtc-linux@googlegroups.com
Signed-off-by: John Stultz <john.stultz@linaro.org>

drivers/rtc/rtc-rp5c01.c

@@ -249,15 +249,15 @@ static int __init rp5c01_rtc_probe(struct platform_device *dev)
 
 	spin_lock_init(&priv->lock);
 
+	platform_set_drvdata(dev, priv);
+
 	rtc = rtc_device_register("rtc-rp5c01", &dev->dev, &rp5c01_rtc_ops,
 				  THIS_MODULE);
 	if (IS_ERR(rtc)) {
 		error = PTR_ERR(rtc);
 		goto out_unmap;
 	}
-
 	priv->rtc = rtc;
-	platform_set_drvdata(dev, priv);
 
 	error = sysfs_create_bin_file(&dev->dev.kobj, &priv->nvram_attr);
 	if (error)
@@ -268,6 +268,7 @@ static int __init rp5c01_rtc_probe(struct platform_device *dev)
 out_unregister:
 	rtc_device_unregister(rtc);
 out_unmap:
+	platform_set_drvdata(dev, NULL);
 	iounmap(priv->regs);
 out_free_priv:
 	kfree(priv);