rtc: m41t80: Initialize clientdata 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 clientdata.

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 clientdata 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-m41t80.c

@@ -783,6 +783,9 @@ static int m41t80_probe(struct i2c_client *client,
 		goto exit;
 	}
 
+	clientdata->features = id->driver_data;
+	i2c_set_clientdata(client, clientdata);
+
 	rtc = rtc_device_register(client->name, &client->dev,
 				  &m41t80_rtc_ops, THIS_MODULE);
 	if (IS_ERR(rtc)) {
@@ -792,8 +795,6 @@ static int m41t80_probe(struct i2c_client *client,
 	}
 
 	clientdata->rtc = rtc;
-	clientdata->features = id->driver_data;
-	i2c_set_clientdata(client, clientdata);
 
 	/* Make sure HT (Halt Update) bit is cleared */
 	rc = i2c_smbus_read_byte_data(client, M41T80_REG_ALARM_HOUR);