tools/target_dec_fuzzer: Adjust threshold for VMIX
Fixes: Timeout
Fixes: 62286/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_VMIX_fuzzer-5155237134204928
Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit aa1e768120
)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>