rtc: ep93xx: Initialize drvdata before registering device

Commit f44f7f9 ("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: Alessandro Zummo <a.zummo@towertech.it>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: rtc-linux@googlegroups.com
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
[Fixed up commit log -jstultz]
Signed-off-by: John Stultz <john.stultz@linaro.org>

drivers/rtc/rtc-ep93xx.c

@@ -151,6 +151,7 @@ static int __init ep93xx_rtc_probe(struct platform_device *pdev)
 		return -ENXIO;
 
 	pdev->dev.platform_data = ep93xx_rtc;
+	platform_set_drvdata(pdev, rtc);
 
 	rtc = rtc_device_register(pdev->name,
 				&pdev->dev, &ep93xx_rtc_ops, THIS_MODULE);
@@ -159,18 +160,16 @@ static int __init ep93xx_rtc_probe(struct platform_device *pdev)
 		goto exit;
 	}
 
-	platform_set_drvdata(pdev, rtc);
-
 	err = sysfs_create_group(&pdev->dev.kobj, &ep93xx_rtc_sysfs_files);
 	if (err)
 		goto fail;
 
 	return 0;
 
 fail:
-	platform_set_drvdata(pdev, NULL);
 	rtc_device_unregister(rtc);
 exit:
+	platform_set_drvdata(pdev, NULL);
 	pdev->dev.platform_data = NULL;
 	return err;
 }