LU-6142 ldlm: Fix style issues for interval_tree.c

LU-6142 ldlm: Fix style issues for interval_tree.c

This patch fixes issues reported by checkpatch
for file lustre/ldlm/interval_tree.c

Test-Parameters: trivial
Change-Id: Ida99aa8f7a5928e87611c73aa7b5d0dc4a5246e9
Signed-off-by: Arshad Hussain <arshad.super@gmail.com>
Reviewed-on: https://review.whamcloud.com/34498
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Ben Evans <bevans@cray.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>