rtc: at91rm9200: remove race condition

While highly unlikely, it is possible to get an interrupt as soon as it is
requested. In that case, at91_rtc_interrupt() will be called with rtc ==
NULL.

Solve that by using devm_rtc_allocate_device/rtc_register_device.
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

drivers/rtc/rtc-at91rm9200.c

@@ -409,6 +409,11 @@ static int __init at91_rtc_probe(struct platform_device *pdev)
 		return -ENOMEM;
 	}
 
+	rtc = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(rtc))
+		return PTR_ERR(rtc);
+	platform_set_drvdata(pdev, rtc);
+
 	sclk = devm_clk_get(&pdev->dev, NULL);
 	if (IS_ERR(sclk))
 		return PTR_ERR(sclk);
@@ -441,13 +446,10 @@ static int __init at91_rtc_probe(struct platform_device *pdev)
 	if (!device_can_wakeup(&pdev->dev))
 		device_init_wakeup(&pdev->dev, 1);
 
-	rtc = devm_rtc_device_register(&pdev->dev, pdev->name,
-				&at91_rtc_ops, THIS_MODULE);
-	if (IS_ERR(rtc)) {
-		ret = PTR_ERR(rtc);
+	rtc->ops = &at91_rtc_ops;
+	ret = rtc_register_device(rtc);
+	if (ret)
 		goto err_clk;
-	}
-	platform_set_drvdata(pdev, rtc);
 
 	/* enable SECEV interrupt in order to initialize at91_rtc_upd_rdy
 	 * completion.