net/mlx5: CT: Fix missing cleanup of ct nat table on init failure

If CT fails to initialize it's rhashtables, it doesn't destroy
the ct nat global table.

Destroy the ct nat global table on ct init failure.

Fixes: d7cade51 ("net/mlx5e: check return value of rhashtable_init")
Signed-off-by: Paul Blakey <paulb@nvidia.com>
Reviewed-by: Oz Shlomo <ozsh@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>