tools/target_dec_fuzzer: Adjust VP4 threshold

Fixes: Timeout (>10sec -> <100ms)
Fixes: 31515/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_VP4_fuzzer-5247114134290432

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

tools/target_dec_fuzzer.c

@@ -192,6 +192,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
     case AV_CODEC_ID_TRUEMOTION2: maxpixels  /= 1024;  break;
     case AV_CODEC_ID_VC1IMAGE:    maxpixels  /= 8192;  break;
     case AV_CODEC_ID_VMNC:        maxpixels  /= 8192;  break;
+    case AV_CODEC_ID_VP4:         maxpixels  /= 4096;  break;
     case AV_CODEC_ID_VP7:         maxpixels  /= 256;   break;
     case AV_CODEC_ID_VP9:         maxpixels  /= 4096;  break;
     case AV_CODEC_ID_WAVPACK:     maxsamples /= 1024;  break;