powerpc/kdump64: Don't reference freed memory as pacas

Starting with 1426d5a3 (powerpc:
Dynamically allocate pacas) the space for pacas beyond cpu_possible
is freed, but we failed to update the loop in crash.c.

Since c1854e00 (powerpc: Set nr_cpu_ids
early and use it to free PACAs) the number of pacas allocated is
always nr_cpu_ids.
Signed-off-by: Milton Miller <miltonm@bga.com>
Cc: <stable@kernel.org> # .34.x
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/crash.c

@@ -236,7 +236,7 @@ static void crash_kexec_wait_realmode(int cpu)
 	int i;
 
 	msecs = 10000;
-	for (i=0; i < NR_CPUS && msecs > 0; i++) {
+	for (i=0; i < nr_cpu_ids && msecs > 0; i++) {
 		if (i == cpu)
 			continue;