avcodec/aacps: fix number of bands used with ipd/opd

Fixes use of uninitialized memory
Fixes: msan_uninit-mem_7f861d16355f_1664_File1_fixed.aac
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>