LU-16565 ldlm: Add ldlm_is,set,clear to spelling

LU-16565 ldlm: Add ldlm_is,set,clear to spelling

Prior to removing the ldlm flag macros, add them to spelling.txt

Test-Parameters: trivial
Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: Ic0fcfb7603c956010e90812338bec38964e815ce
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/50030
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>