net/mlx5: Avoid double free of root ns in the error flow path

When root ns setup for rdma, sniffer tx and sniffer rx fails,
such root ns cleanup is done by the error unwinding path of
mlx5_cleanup_fs().
Below call graph shows an example for sniffer_rx_root_ns.

mlx5_init_fs()
  init_sniffer_rx_root_ns()
    cleanup_root_ns(steering->sniffer_rx_root_ns);
mlx5_cleanup_fs()
  cleanup_root_ns(steering->sniffer_rx_root_ns);
  /* double free of sniffer_rx_root_ns */

Hence, use the existing cleanup_fs to cleanup.

Fixes: d83eb50e ("net/mlx5: Add support in RDMA RX steering")
Fixes: 87d22483 ("net/mlx5: Add sniffer namespaces")
Signed-off-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>