slub: add missing __percpu markup in mm/slub_def.h

kmem_cache->cpu_slab is a percpu pointer but was missing __percpu
markup.  Add it.

Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index 6447a72..5ec4bc0 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -68,7 +68,7 @@
  * Slab cache management.
  */
 struct kmem_cache {
-	struct kmem_cache_cpu *cpu_slab;
+	struct kmem_cache_cpu __percpu *cpu_slab;
 	/* Used for retriving partial slabs etc */
 	unsigned long flags;
 	int size;		/* The size of an object including meta data */