powerpc/numa: Fix bug in unmap_cpu_from_node

When converting to the new cpumask code I screwed up:

-       if (cpu_isset(cpu, numa_cpumask_lookup_table[node])) {
-               cpu_clear(cpu, numa_cpumask_lookup_table[node]);
+       if (cpumask_test_cpu(cpu, node_to_cpumask_map[node])) {
+               cpumask_set_cpu(cpu, node_to_cpumask_map[node]);

This was introduced in commit 25863de0 (powerpc/cpumask: Convert NUMA code
to new cpumask API)

Fix it.
Signed-off-by: Anton Blanchard <anton@samba.org>
Cc: <stable@kernel.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/mm/numa.c

@@ -186,7 +186,7 @@ static void unmap_cpu_from_node(unsigned long cpu)
 	dbg("removing cpu %lu from node %d\n", cpu, node);
 
 	if (cpumask_test_cpu(cpu, node_to_cpumask_map[node])) {
-		cpumask_set_cpu(cpu, node_to_cpumask_map[node]);
+		cpumask_clear_cpu(cpu, node_to_cpumask_map[node]);
 	} else {
 		printk(KERN_ERR "WARNING: cpu %lu not found in node %d\n",
 		       cpu, node);