maple_tree: clean up mas_dfs_postorder()

Convert loop type to ensure all variables are set to make the compiler
happy, and use the mas_is_none() function instead of explicitly checking
the node in the maple state.

Link: https://lkml.kernel.org/r/20230518145544.1722059-5-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: David Binderman <dcb314@hotmail.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Vernon Yang <vernon2gm@gmail.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

lib/maple_tree.c

@@ -6734,15 +6734,12 @@ static void mas_dfs_postorder(struct ma_state *mas, unsigned long max)
 
 	mas->node = mn;
 	mas_ascend(mas);
-	while (mas->node != MAS_NONE) {
+	do {
 		p = mas->node;
 		p_min = mas->min;
 		p_max = mas->max;
 		mas_prev_node(mas, 0);
-	}
-
-	if (p == MAS_NONE)
-		return;
+	} while (!mas_is_none(mas));
 
 	mas->node = p;
 	mas->max = p_max;