The function mlx5_query_nic_vport_node_guid() calls the functuion
mlx5_query_nic_vport_context() but does not check its return value.
A proper implementation can be found in mlx5_nic_vport_query_local_lb().
Add error handling for mlx5_query_nic_vport_context(). If it fails, free
the out buffer via kvfree() and return error code.
Fixes: 9efa75254593 ("net/mlx5_core: Introduce access functions to query vport RoCE fields")