net/mlx5: Fix mlx5_vport_tbl_attr chain from u16 to u32

The offending refactor commit uses u16 chain wrongly. Actually, it
should be u32.

Fixes: c620b772 ("net/mlx5: Refactor tc flow attributes structure")
CC: Ariel Levkovich <lariel@nvidia.com>
Signed-off-by: Chris Mi <cmi@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>