LU-14980 mdd: unlock object before changelog

LU-14980 mdd: unlock object before changelog

we can't hold the object (osd) lock over transaction start
due to the locking rules. and we don't need the object
to be locked as only the fid is used at that point.

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: Iaeb4645bfc9271d21d3644398c4c83f8e9b7aa04
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/44828
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Mikhail Pershin <mpershin@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>