x86/apic: Use this_cpu_ptr() in local_timer_interrupt()

Accessing the per cpu data via per_cpu(, smp_processor_id()) is
pointless. Use this_cpu_ptr() instead.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20170828064956.829552757@linutronix.deSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/apic/apic.c

@@ -988,8 +988,7 @@ void setup_secondary_APIC_clock(void)
  */
 static void local_apic_timer_interrupt(void)
 {
-	int cpu = smp_processor_id();
-	struct clock_event_device *evt = &per_cpu(lapic_events, cpu);
+	struct clock_event_device *evt = this_cpu_ptr(&lapic_events);
 
 	/*
 	 * Normally we should not be here till LAPIC has been initialized but
@@ -1003,7 +1002,8 @@ static void local_apic_timer_interrupt(void)
 	 * spurious.
 	 */
 	if (!evt->event_handler) {
-		pr_warning("Spurious LAPIC timer interrupt on cpu %d\n", cpu);
+		pr_warning("Spurious LAPIC timer interrupt on cpu %d\n",
+			   smp_processor_id());
 		/* Switch it off */
 		lapic_timer_shutdown(evt);
 		return;