net/mlx5: Fix null-ptr-deref in mlx5_create_{inner_,}ttc_table()

In the Linux kernel, the following vulnerability has been resolved:

net/mlx5: Fix null-ptr-deref in mlx5_create_{inner_,}ttc_table()

Add NULL check for mlx5_get_flow_namespace() returns in

mlx5_create_inner_ttc_table() and mlx5_create_ttc_table() to prevent

NULL pointer dereference.