rtc: Fix possible null pointer dereference in rtc-mpc5121.c

Mark Loard pointed out:
"For example, this beauty from rtc-mpc5121.c in the same update:
...
rtc->rtc = rtc_device_register("mpc5200-rtc", &op->dev,
&mpc5200_rtc_ops, THIS_MODULE);
...

rtc->rtc->uie_unsupported = 1; // <<<< Ooops NULL pointer >>>>

if (IS_ERR(rtc->rtc)) { // <<<< this needs to be earlier >>>>
err = PTR_ERR(rtc->rtc);
goto out_free_irq;
}
..."

This patch moves setting the uie_unsupported flag to after we validate
the rtc->rtc pointer to resolve this.

Reported by: Mark Lord <[e-mail]>
Signed-off-by: John Stultz <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Thomas Gleixner <[e-mail]>

drivers/rtc/rtc-mpc5121.c

···
 						&mpc5200_rtc_ops, THIS_MODULE);
 	}
 
-	rtc->rtc->uie_unsupported = 1;
-
 	if (IS_ERR(rtc->rtc)) {
 		err = PTR_ERR(rtc->rtc);
 		goto out_free_irq;
 	}
+	rtc->rtc->uie_unsupported = 1;
 
 	return 0;