slab: use 32-bit arithmetic in freelist_randomize()

SLAB doesn't support 4GB+ of objects per slab, therefore randomization
doesn't need size_t.

Link: http://lkml.kernel.org/r/20180305200730.15812-25-adobriyan@gmail.com
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/slab_common.c

@@ -1186,10 +1186,10 @@ EXPORT_SYMBOL(kmalloc_order_trace);
 #ifdef CONFIG_SLAB_FREELIST_RANDOM
 /* Randomize a generic freelist */
 static void freelist_randomize(struct rnd_state *state, unsigned int *list,
-			size_t count)
+			       unsigned int count)
 {
-	size_t i;
 	unsigned int rand;
+	unsigned int i;
 
 	for (i = 0; i < count; i++)
 		list[i] = i;