IB/cm: Simplify ib_cancel_mad() and ib_modify_mad() calls

The mad_agent parameter is redundant since the struct ib_mad_send_buf
already has a pointer of it.

Link: https://lore.kernel.org/r/0987c784b25f7bfa72f78691f50cff066de587e1.1622629024.git.leonro@nvidia.com


Signed-off-by: Mark Zhang <markzhang@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>