[S390] Cleanup xtime usage

This replaces direct xtime usage in the s390 arch with timekeeping accessors,
so we can further clean up the timekeeping core.

Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/time.c

@@ -73,15 +73,15 @@ unsigned long long monotonic_clock(void)
 }
 EXPORT_SYMBOL(monotonic_clock);
 
-void tod_to_timeval(__u64 todval, struct timespec *xtime)
+void tod_to_timeval(__u64 todval, struct timespec *xt)
 {
 	unsigned long long sec;
 
 	sec = todval >> 12;
 	do_div(sec, 1000000);
-	xtime->tv_sec = sec;
+	xt->tv_sec = sec;
 	todval -= (sec * 1000000) << 12;
-	xtime->tv_nsec = ((todval * 1000) >> 12);
+	xt->tv_nsec = ((todval * 1000) >> 12);
 }
 EXPORT_SYMBOL(tod_to_timeval);
 
@@ -216,8 +216,8 @@ void update_vsyscall(struct timespec *wall_time, struct clocksource *clock,
 	++vdso_data->tb_update_count;
 	smp_wmb();
 	vdso_data->xtime_tod_stamp = clock->cycle_last;
-	vdso_data->xtime_clock_sec = xtime.tv_sec;
-	vdso_data->xtime_clock_nsec = xtime.tv_nsec;
+	vdso_data->xtime_clock_sec = wall_time->tv_sec;
+	vdso_data->xtime_clock_nsec = wall_time->tv_nsec;
 	vdso_data->wtom_clock_sec = wall_to_monotonic.tv_sec;
 	vdso_data->wtom_clock_nsec = wall_to_monotonic.tv_nsec;
 	smp_wmb();