percpu: make pcpu_free_chunk() use pcpu_mem_free() instead of kfree()

commit 099a19d('allow limited allocation before slab is online') made
pcpu_alloc_chunk() use pcpu_mem_zalloc() but forgot to update
pcpu_free_chunk() accordingly.  This doesn't cause any immediate
problema, but fix it for consistency.

tj: commit message updated

Signed-off-by: Joonsoo Kim <js1304@gmail.com>
Cc: Christoph Lameter <cl@linux.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

mm/percpu.c

@@ -631,7 +631,7 @@ static void pcpu_free_chunk(struct pcpu_chunk *chunk)
 	if (!chunk)
 		return;
 	pcpu_mem_free(chunk->map, chunk->map_alloc * sizeof(chunk->map[0]));
-	kfree(chunk);
+	pcpu_mem_free(chunk, pcpu_chunk_struct_size);
 }
 
 /*