LU-18461 lod: convert a lti_ea_store to the lu_buf

LU-18461 lod: convert a lti_ea_store to the lu_buf

lti_ea_store + lti_ea_store_size is same as lu_buf,
lets reuse code.

Signed-off-by: Alexey Lyashkov <alexey.lyashkov@hpe.com>
Change-Id: I61334247288736286937eeb0bb3afee0638c28bb
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/57187
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Timothy Day <timday@amazon.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>