tools/target_dec_fuzzer: Adjust threshold for MVHA

Fixes: Timeout
Fixes: 62120/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MVHA_fuzzer-5647877768347648

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 6359b2ce03)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

tools/target_dec_fuzzer.c

@@ -258,6 +258,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
     case AV_CODEC_ID_MSZH:        maxpixels  /= 128;   break;
     case AV_CODEC_ID_MTS2:        maxpixels  /= 4096;  break;
     case AV_CODEC_ID_MVC2:        maxpixels  /= 128;   break;
+    case AV_CODEC_ID_MVHA:        maxpixels  /= 16384; break;
     case AV_CODEC_ID_MVDV:        maxpixels  /= 1024;  break;
     case AV_CODEC_ID_MWSC:        maxpixels  /= 256;   break;
     case AV_CODEC_ID_MXPEG:       maxpixels  /= 128;   break;