net/mlx5e: kTLS, Fix tisn field name

Use the proper tisn field name from the union in struct mlx5_wqe_ctrl_seg.

Fixes: d2ead1f3

 ("net/mlx5e: Add kTLS TX HW offload support")
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>