LU-6142 osd: Fix style issues for osd_index.c

LU-6142 osd: Fix style issues for osd_index.c

This patch fixes issues reported by checkpatch
for file lustre/osd-zfs/osd_index.c

Test-Parameters: trivial fstype=zfs
Signed-off-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Change-Id: If2fa688443dd2d7528b6c2551f4f6cd21e39e8b3
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/54231
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Timothy Day <timday@amazon.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>