RDMA/mlx5: Use correct device num_ports when modify DC

RDMA/mlx5: Use correct device num_ports when modify DC

Just like other QP types, when modify DC, the port_num should be compared
with dev->num_ports, instead of HCA_CAP.num_ports.  Otherwise Multi-port
vHCA on DC may not work.

Fixes: 776a3906b692 ("IB/mlx5: Add support for DC target QP")
Link: https://lore.kernel.org/r/20230420013906.1244185-1-markzhang@nvidia.com
Signed-off-by: Mark Zhang <markzhang@nvidia.com>
Reviewed-by: Maor Gottlieb <maorg@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>