x86: remove get_cycles_sync

rdtsc is now speculation-safe, so no need for the sync variants of
the APIs.

[ mingo@elte.hu: removed the nsec_barrier() complication. ]

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/arch/x86/kernel/time_64.c b/arch/x86/kernel/time_64.c
index 91d4d49..61b17f5 100644
--- a/arch/x86/kernel/time_64.c
+++ b/arch/x86/kernel/time_64.c
@@ -83,7 +83,7 @@
 	rdtscl(tsc_start);
 	do {
 		rdmsrl(MSR_K7_PERFCTR0 + i, pmc_now);
-		tsc_now = get_cycles_sync();
+		tsc_now = get_cycles();
 	} while ((tsc_now - tsc_start) < TICK_COUNT);
 
 	local_irq_restore(flags);