mm/mempolicy.c: use enum value MPOL_REBIND_ONCE in mpol_rebind_policy()

We have enum definition in mempolicy.h: MPOL_REBIND_ONCE.  It should
replace the magic number 0 for step comparison in function
mpol_rebind_policy.
Signed-off-by: Wang Sheng-Hui <shhuiw@gmail.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/mempolicy.c

@@ -390,7 +390,7 @@ static void mpol_rebind_policy(struct mempolicy *pol, const nodemask_t *newmask,
 {
 	if (!pol)
 		return;
-	if (!mpol_store_user_nodemask(pol) && step == 0 &&
+	if (!mpol_store_user_nodemask(pol) && step == MPOL_REBIND_ONCE &&
 	    nodes_equal(pol->w.cpuset_mems_allowed, *newmask))
 		return;