Fix unreg_umr to ignore the mkey state and do not fail if was freed.  This
prevents a case that a user space application already changed the mkey
state to free and then the UMR operation will fail leaving the mkey in an
inappropriate state.

Link: https://lore.kernel.org/r/20190723065733.4899-3-leon@kernel.org
Cc: <stable@vger.kernel.org> # 3.19
Fixes: 968e78dd ("IB/mlx5: Enhance UMR support to allow partial page table update")
Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
Reviewed-by: Artemy Kovalyov <artemyko@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>