x86, tsc: Fix a preemption leak in restore_sched_clock_state()

A real life genuine preemption leak..
Reported-and-tested-by: Jeff Chua <jeff.chua.linux@gmail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/x86/kernel/tsc.c

@@ -655,7 +655,7 @@ void restore_sched_clock_state(void)
 
 	local_irq_save(flags);
 
-	get_cpu_var(cyc2ns_offset) = 0;
+	__get_cpu_var(cyc2ns_offset) = 0;
 	offset = cyc2ns_suspend - sched_clock();
 
 	for_each_possible_cpu(cpu)