ubifs: do_rename: Fix wrong space budget when target inode's nlink > 1

ubifs: do_rename: Fix wrong space budget when target inode's nlink > 1

If target inode is a special file (eg. block/char device) with nlink
count greater than 1, the inode with ui->data will be re-written on
disk. However, UBIFS losts target inode's data_len while doing space
budget. 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=216494
Fixes: 1e51764a3c2ac0 ("UBIFS: add new flash file system")
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>