avcodec/hevc_ps: Fix integer overflow with beta/tc offsets

Fixes: runtime error: signed integer overflow: 2113929216 * 2 cannot be represented in type 'int'
Fixes: 2422/clusterfuzz-testcase-minimized-5242114713583616

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