slob: Fix to return wrong pointer

Although slob_alloc return NULL, __kmalloc_node returns NULL + align.
Because align always can be changed, it is very hard for debugging
problem of no page if it don't return NULL.

We have to return NULL in case of no page.

[penberg@cs.helsinki.fi: fix formatting as suggested by Matt.]
Acked-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: MinChan Kim <minchan.kim@gmail.com>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

mm/slob.c

@@ -469,7 +469,8 @@ void *__kmalloc_node(size_t size, gfp_t gfp, int node)
 			return ZERO_SIZE_PTR;
 
 		m = slob_alloc(size + align, gfp, align, node);
-		if (m)
+		if (!m)
+			return NULL;
 		*m = size;
 		return (void *)m + align;
 	} else {