maple_tree: simplify mas_wr_node_walk()

Simplify code of mas_wr_node_walk() without changing functionality, and
improve readability.  Remove some special judgments.  Instead of
dynamically recording the min and max in the loop, get the final min and
max directly at the end.

Link: https://lkml.kernel.org/r/20230314124203.91572-3-zhangpeng.00@bytedance.com


Signed-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>