avcodec/hevc_ps: Fix c?_qp_offset_list size

Fixes: runtime error: index 5 out of bounds for type 'int8_t const[5]'
Fixes:3175/clusterfuzz-testcase-minimized-4736774054084608

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