avcodec/aacps (fixed point): Fix multiple signed integer overflows

Fixes: runtime error: signed integer overflow: 1421978265 - -1810326882 cannot be represented in type 'int'
Fixes: 2527/clusterfuzz-testcase-minimized-5260915396050944

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
