rtc: pcap: 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 <[e-mail]>
CC: Alessandro Zummo <[e-mail]>
CC: Thomas Gleixner <[e-mail]>
CC: [e-mail]
Signed-off-by: John Stultz <[e-mail]>

drivers/rtc/rtc-pcap.c

···
 
 	pcap_rtc->pcap = dev_get_drvdata(pdev->dev.parent);
 
+	platform_set_drvdata(pdev, pcap_rtc);
+
 	pcap_rtc->rtc = rtc_device_register("pcap", &pdev->dev,
 				  &pcap_rtc_ops, THIS_MODULE);
 	if (IS_ERR(pcap_rtc->rtc)) {
···
 		goto fail_rtc;
 	}
 
-	platform_set_drvdata(pdev, pcap_rtc);
 
 	timer_irq = pcap_to_irq(pcap_rtc->pcap, PCAP_IRQ_1HZ);
 	alarm_irq = pcap_to_irq(pcap_rtc->pcap, PCAP_IRQ_TODA);
···
 fail_timer:
 	rtc_device_unregister(pcap_rtc->rtc);
 fail_rtc:
+	platform_set_drvdata(pdev, NULL);
 	kfree(pcap_rtc);
 	return err;
 }