rtc-cmos: do dev_set_drvdata() earlier in the initialization

The bug is an oops when dev_get_drvdata() returned null in
cmos_update_irq_enable().  The call tree looks like this:
  rtc_dev_ioctl()
    => rtc_update_irq_enable()
      => cmos_update_irq_enable()

It's caused by a race condition in the module initialization.  It is
rtc_device_register() which makes the ioctl operations live so I moved
the call to dev_set_drvdata() before the call to rtc_device_register().

Addresses https://bugzilla.kernel.org/show_bug.cgi?id=15963

Reported-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Dan Carpenter <error27@gmail.com>
Tested-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Paul Gortmaker <p_gortmaker@yahoo.com>
Cc: Malte Schroder <maltesch@gmx.de>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Herton Ronaldo Krzesinski <herton@mandriva.com.br>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/rtc-cmos.c

@@ -719,15 +719,16 @@ cmos_do_probe(struct device *dev, struct resource *ports, int rtc_irq)
 		}
 	}
 
+	cmos_rtc.dev = dev;
+	dev_set_drvdata(dev, &cmos_rtc);
+
 	cmos_rtc.rtc = rtc_device_register(driver_name, dev,
 				&cmos_rtc_ops, THIS_MODULE);
 	if (IS_ERR(cmos_rtc.rtc)) {
 		retval = PTR_ERR(cmos_rtc.rtc);
 		goto cleanup0;
 	}
 
-	cmos_rtc.dev = dev;
-	dev_set_drvdata(dev, &cmos_rtc);
 	rename_region(ports, dev_name(&cmos_rtc.rtc->dev));
 
 	spin_lock_irq(&rtc_lock);