avcodec/cfhd: Fix runtime error: signed integer overflow: 65280 * 65288 cannot be represented in type 'int'

Fixes: 1925/clusterfuzz-testcase-minimized-5564569688735744

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