LU-6142 ldlm: minor list_entry improvements in ldlm_request.c

LU-6142 ldlm: minor list_entry improvements in ldlm_request.c

Small clarify improvements, and one local variable avoided.

Linux-commit: cb830bef04f1bd80da7eca3d3edaea590f4b350b

Change-Id: I1a34849adca228a465a2b771fb0aa707a9283c7c
Signed-off-by: Mr. NeilBrown <neilb@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/49738
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>