xfs: fix inode reservation space for removing transaction

In 'fs/xfs/libxfs/xfs_trans_resv.c', the comment for transaction of removing a
directory entry writes:

/* fs/xfs/libxfs/xfs_trans_resv.c begin */
/*
 * For removing a directory entry we can modify:
 *    the parent directory inode: inode size
 *    the removed inode: inode size
...
xfs_calc_remove_reservation(
        struct xfs_mount        *mp)
{
        return XFS_DQUOT_LOGRES(mp) +
                xfs_calc_iunlink_add_reservation(mp) +
                max((xfs_calc_inode_res(mp, 1) +
...
/* fs/xfs/libxfs/xfs_trans_resv.c end */

There has 2 inode size of space to be reserverd, but the actual code
for inode reservation space writes.

There only count for 1 inode size to be reserved in
'xfs_calc_inode_res(mp, 1)', rather than 2.

Signed-off-by: hexiaole <hexiaole@kylinos.cn>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
[djwong: remove redundant code citations]
Signed-off-by: Darrick J. Wong <djwong@kernel.org>