slub: Fix bad boundary check in init_kmem_cache_nodes()

Function init_kmem_cache_nodes is incorrect when checking upper limitation of
kmalloc_caches. The breakage was introduced by commit
91efd773 ("dma kmalloc handling fixes").

Acked-by: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>