rtc: mxc: Initialize drvdata before registering device

Commit f44f7f96a2 ("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-mxc.c

@@ -418,14 +418,6 @@ static int __init mxc_rtc_probe(struct platform_device *pdev)
 		goto exit_put_clk;
 	}
 
-	rtc = rtc_device_register(pdev->name, &pdev->dev, &mxc_rtc_ops,
-				  THIS_MODULE);
-	if (IS_ERR(rtc)) {
-		ret = PTR_ERR(rtc);
-		goto exit_put_clk;
-	}
-
-	pdata->rtc = rtc;
 	platform_set_drvdata(pdev, pdata);
 
 	/* Configure and enable the RTC */
@@ -438,8 +430,19 @@ static int __init mxc_rtc_probe(struct platform_device *pdev)
 		pdata->irq = -1;
 	}
 
+	rtc = rtc_device_register(pdev->name, &pdev->dev, &mxc_rtc_ops,
+				  THIS_MODULE);
+	if (IS_ERR(rtc)) {
+		ret = PTR_ERR(rtc);
+		goto exit_clr_drvdata;
+	}
+
+	pdata->rtc = rtc;
+
 	return 0;
 
+exit_clr_drvdata:
+	platform_set_drvdata(pdev, NULL);
 exit_put_clk:
 	clk_disable(pdata->clk);
 	clk_put(pdata->clk);