tools/target_dec_fuzzer: Adjust threshold for Jpeg2000

Fixes: Timeout
Fixes: 50955/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_JPEG2000_fuzzer-5148704872464384

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

@@ -242,7 +242,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
     case AV_CODEC_ID_IFF_ILBM:    maxpixels  /= 128;   break;
     case AV_CODEC_ID_INDEO4:      maxpixels  /= 128;   break;
     case AV_CODEC_ID_INTERPLAY_ACM: maxsamples /= 16384;  break;
-    case AV_CODEC_ID_JPEG2000:    maxpixels  /= 16;    break;
+    case AV_CODEC_ID_JPEG2000:    maxpixels  /= 4096;  break;
     case AV_CODEC_ID_LAGARITH:    maxpixels  /= 1024;  break;
     case AV_CODEC_ID_LOCO:        maxpixels  /= 1024;  break;
     case AV_CODEC_ID_VORBIS:      maxsamples /= 1024;  break;