LU-6142 obdclass: Fix style issues for lustre_idmap.h

LU-6142 obdclass: Fix style issues for lustre_idmap.h

This patch fixes issues reported by checkpatch
for file lustre/include/lustre_idmap.h

Test-Parameters: trivial
Signed-off-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Change-Id: I975d7f719bb2841db93c6b9cda530e02984d9ca3
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/53913
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>