IB/mlx5: Avoid unnecessary typecast

IB device pointer is already available while deallocating IB device,
Hence do not typecast it.

Link: https://lore.kernel.org/r/20190723065733.4899-9-leon@kernel.org


Signed-off-by: Parav Pandit <parav@mellanox.com>
Reviewed-by: Daniel Jurgens <danielj@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>