net/mlx5: Fix root flow table update

When we destroy the last flow table we need to update
the root_ft to NULL.

It fixes an issue for when the last flow table is destroyed
and recreated again, root_ft pointer will not be updated,
as a result traffic will be dropped.

Fixes: 2cc43b4 ('net/mlx5_core: Managing root flow table')
Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlx5/core/fs_core.c

@@ -1292,8 +1292,8 @@ static int update_root_ft_destroy(struct mlx5_flow_table *ft)
 				       ft->id);
 			return err;
 		}
-		root->root_ft = new_root_ft;
 	}
+	root->root_ft = new_root_ft;
 	return 0;
 }