mtrr atomicity fix

Rafael gets this on an SMP box with kernel preemption enabled, during
hibernation and restore (100% of the time):

Enabling non-boot CPUs ...
BUG: using smp_processor_id() in preemptible [00000001] code: bash/4514
caller is mtrr_save_state+0x9/0x40

Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/i386/kernel/cpu/mtrr/main.c

@@ -734,10 +734,13 @@ void mtrr_ap_init(void)
  */
 void mtrr_save_state(void)
 {
-	if (smp_processor_id() == 0)
+	int cpu = get_cpu();
+
+	if (cpu == 0)
 		mtrr_save_fixed_ranges(NULL);
 	else
 		smp_call_function_single(0, mtrr_save_fixed_ranges, NULL, 1, 1);
+	put_cpu();
 }
 
 static int __init mtrr_init_finialize(void)