rtc: test before subtraction on unsigned

new_alarm is unsigned so test before the subtraction.

[akpm@linux-foundation.org: time-wrapping fix]
Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Cc: David Brownell <david-b@pacbell.net>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/rtc-ds1374.c

@@ -222,16 +222,16 @@ static int ds1374_set_alarm(struct device *dev, struct rtc_wkalrm *alarm)
 	rtc_tm_to_time(&alarm->time, &new_alarm);
 	rtc_tm_to_time(&now, &itime);
 
-	new_alarm -= itime;
-
 	/* This can happen due to races, in addition to dates that are
 	 * truly in the past.  To avoid requiring the caller to check for
 	 * races, dates in the past are assumed to be in the recent past
 	 * (i.e. not something that we'd rather the caller know about via
 	 * an error), and the alarm is set to go off as soon as possible.
 	 */
-	if (new_alarm <= 0)
+	if (time_before_eq(new_alarm, itime))
 		new_alarm = 1;
+	else
+		new_alarm -= itime;
 
 	mutex_lock(&ds1374->mutex);