dlm: memory leaks on error path in dlm_user_request()

According to comment in dlm_user_request() ua should be freed
in dlm_free_lkb() after successful attach to lkb.

However ua is attached to lkb not in set_lock_args() but later,
inside request_lock().

Fixes 597d0cae ("[DLM] dlm: user locks")
Cc: stable@kernel.org # 2.6.19

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