powerpc: fix memory corruption by pnv_alloc_idle_core_states

Space allocated for paca is based off nr_cpu_ids,
but pnv_alloc_idle_core_states() iterates paca with
cpu_nr_cores()*threads_per_core, which is using NR_CPUS.

This causes pnv_alloc_idle_core_states() to write over memory,
which is outside of paca array and may later lead to various panics.

Fixes: 7cba160a (powernv/cpuidle: Redesign idle states management)
Signed-off-by: Jan Stancek <jstancek@redhat.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/cputhreads.h

@@ -55,7 +55,7 @@ static inline cpumask_t cpu_thread_mask_to_cores(const struct cpumask *threads)
 
 static inline int cpu_nr_cores(void)
 {
-	return NR_CPUS >> threads_shift;
+	return nr_cpu_ids >> threads_shift;
 }
 
 static inline cpumask_t cpu_online_cores_map(void)