net/mlx5e: CT: Avoid false warning about rule may be used uninitialized

Avoid gcc warning by preset rule to invalid ptr.

Fixes: 4c3844d9 ("net/mlx5e: CT: Introduce connection tracking")
Signed-off-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>