ubifs: Rectify space budget for ubifs_symlink() if symlink is encrypted

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

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Fix bad space budget when symlink file is encrypted. Bad space budget
may let make_reservation() return with -ENOSPC, which could turn ubifs
to read-only mode in do_writepage() process.

Fetch a reproducer in [Link].

Link: https://bugzilla.kernel.org/show_bug.cgi?id=216490


Fixes: ca7f85be ("ubifs: Add support for encrypted symlinks")
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>