LU-17672 ldiskfs: release s_mb_prealloc_table

LU-17672 ldiskfs: release s_mb_prealloc_table

at umount

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: I0a5cbf646c9bd73461691c49c6e7a509acd5a500
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/54553
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>