fft-test: Pass the right struct members instead of casting
Merge commit '165e9df19567ec0b6abee1ee2c26027e6d7aa7bf'

* commit '165e9df19567ec0b6abee1ee2c26027e6d7aa7bf':
  fft-test: Pass the right struct members instead of casting

Merged-by: Michael Niedermayer <michaelni@gmx.at>
avutil/opt: ensure the right buffer is used in set_string_number()

Fixes use of uninitialized memory

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>