avcodec/hq_hqa: Fix runtime error: left shift of negative value -207

Fixes: 1375/clusterfuzz-testcase-minimized-6070134701555712

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