ubifs: Rectify space budget for ubifs_xrename()

hulk inclusion
category: bugfix
bugzilla: 187685, https://gitee.com/openeuler/kernel/issues/I5VVZX


CVE: NA

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There is no space budget for ubifs_xrename(). It may let
make_reservation() return with -ENOSPC, which could turn
ubifs to read-only mode in do_writepage() process.
Fix it by adding space budget for ubifs_xrename().

Fixes: 9ec64962 ("ubifs: Implement RENAME_EXCHANGE")
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>