LU-13922 osd-ldiskfs: no need to add OI cache in readdir

LU-13922 osd-ldiskfs: no need to add OI cache in readdir

It's a waste of time to call osd_add_oi_cache() in osd_it_ea_rec(),
because each dirent read will override it.

Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: Iec701bf66153fdf2ba7a3f3b89565381215abf33
Reviewed-on: https://review.whamcloud.com/39782
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Stephane Thiell <sthiell@stanford.edu>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>