LU-6142 ldlm: use list_for_each_entry in ldlm_lock.c

LU-6142 ldlm: use list_for_each_entry in ldlm_lock.c

This makes some slightly-confusing code a bit clearer, and
avoids the need for 'tmp'.

Linux-commit: 557d001aa51fd6171d7a68dec21f8327fc824173

Change-Id: If9d070492e0016fa235fb38726f7c7a3b380d580
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/+/49734
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>