net/mlx5e: QoS, Fix wrongfully setting parent_element_id on MODIFY_SCHEDULING_ELEMENT

According to HW spec parent_element_id field should be reserved (0x0) when calling
MODIFY_SCHEDULING_ELEMENT command.

This patch remove the wrong initialization of reserved field, parent_element_id, on
mlx5_qos_update_node.

Fixes: 214baf22 ("net/mlx5e: Support HTB offload")
Signed-off-by: Maor Dickman <maord@nvidia.com>
Reviewed-by: Eli Cohen <elic@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>