mm/migration: avoid unneeded nodemask_t initialization

Avoid unneeded next_pass and this_pass initialization as they're always
set before using to save possible cpu cycles when there are plenty of
nodes in the system.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Miaohe Lin <[email protected]>
Reviewed-by: Muchun Song <[email protected]>
Reviewed-by: Baolin Wang <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: "Huang, Ying" <[email protected]>
Cc: Zi Yan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

mm/migrate.c

@@ -2345,8 +2345,8 @@ out_clear:
  */
 static void __set_migration_target_nodes(void)
 {
-	nodemask_t next_pass	= NODE_MASK_NONE;
-	nodemask_t this_pass	= NODE_MASK_NONE;
+	nodemask_t next_pass;
+	nodemask_t this_pass;
 	nodemask_t used_targets = NODE_MASK_NONE;
 	int node, best_distance;