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

@@ -4264,19 +4264,21 @@ 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;
-
-	/* 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) &&
-	    !wr_mas->slots[wr_mas->offset_end + 1]) {
-		wr_mas->offset_end++;
-		if (wr_mas->offset_end == wr_mas->node_end)
-			mas->last = mas->max;
-		else
-			mas->last = wr_mas->pivots[wr_mas->offset_end];
-		wr_mas->end_piv = mas->last;
+	} 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) &&
+		    !wr_mas->slots[wr_mas->offset_end + 1]) {
+			wr_mas->offset_end++;
+			if (wr_mas->offset_end == wr_mas->node_end)
+				mas->last = mas->max;
+			else
+				mas->last = wr_mas->pivots[wr_mas->offset_end];
+			wr_mas->end_piv = mas->last;
+		}
 	}
 
 	if (!wr_mas->content) {