avcodec/ivi_dsp: Fix multiple runtime error: left shift of negative value -71

Fixes: 1734/clusterfuzz-testcase-minimized-5385630815092736

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