LU-17911 obdclass: fix faked flexible arrays in jobid

LU-17911 obdclass: fix faked flexible arrays in jobid

To fix the crash caused by issue of faked flexible arrays
in  jobid.

Signed-off-by: Yang Sheng <ys@whamcloud.com>
Change-Id: Iba88582e20dfe38ec060ed9a05ba3d65ee3e31e1
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/55995
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: Jian Yu <yujian@whamcloud.com>