dlm: possible memory leak on error path in create_lkb()

Fixes 3d6aa675 ("dlm: keep lkbs in idr")
Cc: stable@kernel.org # 3.1

Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Signed-off-by: David Teigland <teigland@redhat.com>