IB/cm: Use container_of() instead of typecast

Use container_of() macro to get to timewait info structure instead of
typecasting.

Link: https://lore.kernel.org/r/20191002122517.17721-5-leon@kernel.org


Signed-off-by: Parav Pandit <parav@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>