LU-12828 ldlm: not freed req on enqueue

LU-12828 ldlm: not freed req on enqueue

ldlm_cli_enqueue may allocate a req but failed to allocate a req
slot and returns an errors without freeing the req.

Fixes: 85a12c6c8d ("LU-12828 ldlm: FLOCK request can be processed twice")
Signed-off-by: Vitaly Fertman <c17818@cray.com>
Change-Id: I9663528bbf2bf64f6439fed6c27d0bc3f274b867
HPE-bug-id: LUS-9337
Reviewed-on: https://es-gerrit.dev.cray.com/158433
Reviewed-by: Alexander Boyko <c17825@cray.com>
Reviewed-by: Andriy Skulysh <c17819@cray.com>
Tested-by: Alexander Lezhoev <c17454@cray.com>
Reviewed-on: https://review.whamcloud.com/41818
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Alexander Boyko <alexander.boyko@hpe.com>
Reviewed-by: Andriy Skulysh <askulysh@gmail.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>