tools/target_dec_fuzzer: Adjust threshold for prores

Fixes: Timeout
Fixes: 42072/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_PRORES_fuzzer-4957999452520448

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

@@ -193,6 +193,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
     case AV_CODEC_ID_APNG:        maxpixels  /= 128;   break;
     case AV_CODEC_ID_QTRLE:       maxpixels  /= 16;    break;
     case AV_CODEC_ID_PAF_VIDEO:   maxpixels  /= 16;    break;
+    case AV_CODEC_ID_PRORES:      maxpixels  /= 256;   break;
     case AV_CODEC_ID_RASC:        maxpixels  /= 16;    break;
     case AV_CODEC_ID_SANM:        maxpixels  /= 16;    break;
     case AV_CODEC_ID_SCPR:        maxpixels  /= 32;    break;