um: Convert to use read_persistent_clock

This patch converts the um arch to use read_persistent_clock().
This allows it to avoid accessing xtime and wall_to_monotonic
directly.
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Cc: Jeff Dike <jdike@addtoit.com>
LKML-Reference: <1279068988-21864-8-git-send-email-johnstul@us.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/um/kernel/time.c

@@ -102,16 +102,17 @@ static void __init setup_itimer(void)
 	clockevents_register_device(&itimer_clockevent);
 }
 
+void read_persistent_clock(struct timespec *ts)
+{
+	nsecs = os_nsecs();
+	set_normalized_timespec(ts, nsecs / NSEC_PER_SEC,
+				nsecs % NSEC_PER_SEC);
+}
+
 void __init time_init(void)
 {
 	long long nsecs;
 
 	timer_init();
-
-	nsecs = os_nsecs();
-	set_normalized_timespec(&wall_to_monotonic, -nsecs / NSEC_PER_SEC,
-				-nsecs % NSEC_PER_SEC);
-	set_normalized_timespec(&xtime, nsecs / NSEC_PER_SEC,
-				nsecs % NSEC_PER_SEC);
 	late_time_init = setup_itimer;
 }