net/mlx5: Query correct caps for min msix vectors

The VFs on the host and the embedded CPU platform share function
numbers. Set the ec_vf_function field to query the caps for the correct
function.

Signed-off-by: Daniel Jurgens <danielj@nvidia.com>
Reviewed-by: William Tu <witu@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>