rtc: don't reference bogus function pointer in kdoc

The mentioned function pointer is long gone since early 2011. Remove the
reference in the comment and reword it slightly.

Fixes: 51ba60c5bb ("RTC: Cleanup rtc_class_ops->update_irq_enable()")
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/interface.c

@@ -573,10 +573,9 @@ out:
 	mutex_unlock(&rtc->ops_lock);
 #ifdef CONFIG_RTC_INTF_DEV_UIE_EMUL
 	/*
-	 * Enable emulation if the driver did not provide
-	 * the update_irq_enable function pointer or if returned
-	 * -EINVAL to signal that it has been configured without
-	 * interrupts or that are not available at the moment.
+	 * Enable emulation if the driver returned -EINVAL to signal that it has
+	 * been configured without interrupts or they are not available at the
+	 * moment.
 	 */
 	if (err == -EINVAL)
 		err = rtc_dev_update_irq_enable_emul(rtc, enabled);