staging: lustre: 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'.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>