avcodec/dirac_dwt: initialize support value for fidelity wavelet

Avoids use of uninitialized memory
Fixes: msan_uninit-mem_7f15e1988a6e_2748_RL_420p_ffdirac.drc
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
