avcodec/hevcdsp_template: Fix undefined shift in put_hevc_pel_bi_w_pixels

Fixes: runtime error: left shift of negative value -95
Fixes: 3077/clusterfuzz-testcase-minimized-4684917524922368

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