[PATCH] ia64: make perfmon CONFIG_PREEMPT-safe again

Here's a  fix for non-preemption safety in perfmon.c.

I haven't tried it while running a preemption stress test, but this
allows q-syscollect to work.

arch/ia64/kernel/perfmon.c

@@ -5475,7 +5475,7 @@ pfm_interrupt_handler(int irq, void *arg, struct pt_regs *regs)
 	int this_cpu;
 	int ret;
 
-	this_cpu = smp_processor_id();
+	this_cpu = get_cpu();
 	min      = pfm_stats[this_cpu].pfm_ovfl_intr_cycles_min;
 	max      = pfm_stats[this_cpu].pfm_ovfl_intr_cycles_max;