net/mlx5: Fix vport QoS cleanup on error

When enabling vport QoS fails, the scheduling node was never freed,
causing a leak.

Add the missing free and reset the vport scheduling node pointer to
NULL.

Fixes: be034bab ("net/mlx5: Make vport QoS enablement more flexible for future extensions")
Signed-off-by: Carolina Jubran <cjubran@nvidia.com>
Reviewed-by: Cosmin Ratiu <cratiu@nvidia.com>
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/20250225072608.526866-2-tariqt@nvidia.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>