tools/target_dec_fuzzer: Add threshold for IFF_ILBM

Fixes: Timeout (32 -> 1sec)
Fixes: 20138/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_IFF_ILBM_fuzzer-5634665251864576

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

tools/target_dec_fuzzer.c

@@ -146,6 +146,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
     case AV_CODEC_ID_GDV:         maxpixels  /= 512;   break;
     case AV_CODEC_ID_GIF:         maxpixels  /= 16;    break;
     case AV_CODEC_ID_HNM4_VIDEO:  maxpixels  /= 128;   break;
+    case AV_CODEC_ID_IFF_ILBM:    maxpixels  /= 128;   break;
     case AV_CODEC_ID_INDEO4:      maxpixels  /= 128;   break;
     case AV_CODEC_ID_LSCR:        maxpixels  /= 16;    break;
     case AV_CODEC_ID_MOTIONPIXELS:maxpixels  /= 256;   break;