mm/slab: fix section mismatch warning

Use the new __init_refok marker to avoid the
section mismatch warning from slab.c
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

mm/slab.c

@@ -2037,7 +2037,7 @@ static size_t calculate_slab_order(struct kmem_cache *cachep,
 	return left_over;
 }
 
-static int setup_cpu_cache(struct kmem_cache *cachep)
+static int __init_refok setup_cpu_cache(struct kmem_cache *cachep)
 {
 	if (g_cpucache_up == FULL)
 		return enable_cpucache(cachep);