Finally, the state structure must be destroyed to free up
memory used to store the state, using the third function,
xilinx_ip_xfft_v9_1_destroy_state, called with the
pointer to the existing state structure.
If the generics of the core need to be changed, destroy the existing state structure and create a new state structure using the new generics. There is no way to change the generics of an existing state structure.