maple_tree: rework mtree_alloc_{range,rrange}()

maple_tree: rework mtree_alloc_{range,rrange}()

Patch series "Clean ups for maple tree", v4.

Some clean ups, mainly to make the code of maple tree more concise.
This patchset has passed the self-test.

This patch (of 10):

Use mas_empty_area{_rev}() to refactor mtree_alloc_{range,rrange}()

Link: https://lkml.kernel.org/r/20230524031247.65949-2-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>