RDMA/mlx5: Fix mlx5 rates to IB rates map

Correct the map between mlx5 rates and corresponding ib rates, as they
don't always have a fixed offset between them.

Fixes: e126ba97 ("mlx5: Add driver for Mellanox Connect-IB adapters")
Link: https://lore.kernel.org/r/20210304124517.1100608-4-leon@kernel.org


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