LU-6142 mdt: Fix style issues for mdt_xattr.c

LU-6142 mdt: Fix style issues for mdt_xattr.c

This patch fixes issues reported by checkpatch
for file lustre/mdt/mdt_xattr.c

Test-Parameters: trivial
Signed-off-by: Arshad Hussain <arshad.super@gmail.com>
Change-Id: I9c832d75f416998e1fbd9d25b5b3f0d3d6cf8b4d
Reviewed-on: https://review.whamcloud.com/38785
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Ben Evans <beevans@whamcloud.com>
Reviewed-by: Petros Koutoupis <petros.koutoupis@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>