net/mlx5: Fix leak upon failure of rule creation

When creation of a new rule that requires allocation of an FTE fails,
need to call to tree_put_node on the FTE in order to release its'
resource.

Fixes: cefc2355

 ("net/mlx5: Fix FTE cleanup")
Signed-off-by: Maor Gottlieb <maorg@nvidia.com>
Reviewed-by: Alaa Hleihel <alaa@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>