avcodec/hevcdsp_template: Fix undefined shift in put_hevc_qpel_bi_w_hv()

Fixes: runtime error: left shift of negative value -3
Fixes: 4524/clusterfuzz-testcase-minimized-6055590120914944

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