rtc: pl031: use RTC_FEATURE_ALARM

Clear RTC_FEATURE_ALARM instead of setting set_alarm, read_alarm and
alarm_irq_enable to NULL.
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20210110231752.1418816-3-alexandre.belloni@bootlin.com

drivers/rtc/rtc-pl031.c

@@ -352,12 +352,8 @@ static int pl031_probe(struct amba_device *adev, const struct amba_id *id)
 		}
 	}
 
-	if (!adev->irq[0]) {
-		/* When there's no interrupt, no point in exposing the alarm */
-		ops->read_alarm = NULL;
-		ops->set_alarm = NULL;
-		ops->alarm_irq_enable = NULL;
-	}
+	if (!adev->irq[0])
+		clear_bit(RTC_FEATURE_ALARM, ldata->rtc->features);
 
 	device_init_wakeup(&adev->dev, true);
 	ldata->rtc = devm_rtc_allocate_device(&adev->dev);