maple_tree: make the code symmetrical in mas_wr_extend_null()

Just make the code symmetrical to improve readability.

Link: https://lkml.kernel.org/r/20230524031247.65949-6-zhangpeng.00@bytedance.comSigned-off-by: Peng Zhang <zhangpeng.00@bytedance.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

lib/maple_tree.c

@@ -4264,9 +4264,10 @@ static inline void mas_wr_extend_null(struct ma_wr_state *wr_mas)
 {
 	struct ma_state *mas = wr_mas->mas;
 
-	if (mas->last < wr_mas->end_piv && !wr_mas->slots[wr_mas->offset_end])
+	if (!wr_mas->slots[wr_mas->offset_end]) {
+		/* If this one is null, the next and prev are not */
 		mas->last = wr_mas->end_piv;
-
+	} else {
 		/* Check next slot(s) if we are overwriting the end */
 		if ((mas->last == wr_mas->end_piv) &&
 		    (wr_mas->node_end != wr_mas->offset_end) &&
@@ -4278,6 +4279,7 @@ static inline void mas_wr_extend_null(struct ma_wr_state *wr_mas)
 				mas->last = wr_mas->pivots[wr_mas->offset_end];
 			wr_mas->end_piv = mas->last;
 		}
+	}
 
 	if (!wr_mas->content) {
 		/* If this one is null, the next and prev are not */