[S390] Fix cpu hotplug (missing 'online' attribute).

72486f1f inverts the logic if an
'online' attribute in /sys/devices/system/cpu/cpuX should appear.
So we end up with no hotpluggable cpus at all...
Set the hotpluggable value to one to make sure the online
attribute appears again.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/smp.c

@@ -794,7 +794,10 @@ static int __init topology_init(void)
 	int ret;
 
 	for_each_possible_cpu(cpu) {
-		ret = register_cpu(&per_cpu(cpu_devices, cpu), cpu);
+		struct cpu *c = &per_cpu(cpu_devices, cpu);
+
+		c->hotpluggable = 1;
+		ret = register_cpu(c, cpu);
 		if (ret)
 			printk(KERN_WARNING "topology_init: register_cpu %d "
 			       "failed (%d)\n", cpu, ret);