mm/slub: Use kmem_cache for the kmem_cache structure

Do not use kmalloc() but kmem_cache_alloc() for the allocation
of the kmem_cache structures in slub.

Reviewed-by: Glauber Costa <glommer@parallels.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
backported for Linux 3.4

Change-Id: Ia2784f4b2253311b1be5535caffdd0d47b51f069
Signed-off-by: Paul Reioux <reioux@gmail.com>