slub: remove impossible condition

`s' cannot be NULL if kmalloc_caches is not NULL.

This conditional would trigger a NULL pointer on `s', anyway, since it is
immediately derefernced if true.
Acked-by: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

mm/slub.c

@@ -2641,7 +2641,7 @@ static noinline struct kmem_cache *dma_kmalloc_cache(int index, gfp_t flags)
 	if (slab_state >= SYSFS)
 		slabflags |= __SYSFS_ADD_DEFERRED;
 
-	if (!s || !text || !kmem_cache_open(s, flags, text,
+	if (!text || !kmem_cache_open(s, flags, text,
 			realsize, ARCH_KMALLOC_MINALIGN, slabflags, NULL)) {
 		s->size = 0;
 		kfree(text);