net/mlx5e: Use struct assignment to initialize mlx5e_tx_wqe_info

Struct assignment guarantees that all fields of the structure are
initialized (those that are not mentioned are zeroed). It makes code
mode robust and reduces chances for unpredictable behavior when one
forgets to reset some field and it holds an old value from previous
iterations of using the structure.

Signed-off-by: Maxim Mikityanskiy <maximmi@mellanox.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>