[S390] correct ktime to tod clock comparator conversion

The conversion of the ktime to a value suitable for the clock comparator
does not take changes to wall_to_monotonic into account. In fact the
conversion just needs the boot clock (sched_clock_base_cc) and the
total_sleep_time.

This is applicable to 3.2+ kernels.

CC: stable@vger.kernel.org
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/time.c

@@ -113,11 +113,14 @@ static void fixup_clock_comparator(unsigned long long delta)
 static int s390_next_ktime(ktime_t expires,
 			   struct clock_event_device *evt)
 {
+	struct timespec ts;
 	u64 nsecs;
 
-	nsecs = ktime_to_ns(ktime_sub(expires, ktime_get_monotonic_offset()));
+	ts.tv_sec = ts.tv_nsec = 0;
+	monotonic_to_bootbased(&ts);
+	nsecs = ktime_to_ns(ktime_add(timespec_to_ktime(ts), expires));
 	do_div(nsecs, 125);
-	S390_lowcore.clock_comparator = TOD_UNIX_EPOCH + (nsecs << 9);
+	S390_lowcore.clock_comparator = sched_clock_base_cc + (nsecs << 9);
 	set_clock_comparator(S390_lowcore.clock_comparator);
 	return 0;
 }