slab: fix DEBUG_SLAB warning

In commit c225150b "slab: fix DEBUG_SLAB build",
"if ((unsigned long)objp & (ARCH_SLAB_MINALIGN-1))" is always true if
ARCH_SLAB_MINALIGN == 0. Do not print warning if ARCH_SLAB_MINALIGN == 0.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

mm/slab.c

@@ -3155,7 +3155,8 @@ static void *cache_alloc_debugcheck_after(struct kmem_cache *cachep,
 	objp += obj_offset(cachep);
 	if (cachep->ctor && cachep->flags & SLAB_POISON)
 		cachep->ctor(objp);
-	if ((unsigned long)objp & (ARCH_SLAB_MINALIGN-1)) {
+	if (ARCH_SLAB_MINALIGN &&
+	    ((unsigned long)objp & (ARCH_SLAB_MINALIGN-1))) {
 		printk(KERN_ERR "0x%p: not aligned to ARCH_SLAB_MINALIGN=%d\n",
 		       objp, (int)ARCH_SLAB_MINALIGN);
 	}