tools/target_dec_fuzzer: Adjust threshold for DST

Fixes: Timeout (too long -> 3sec)
Fixes: 24239/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_DST_fuzzer-5189061015502848

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

tools/target_dec_fuzzer.c

@@ -149,7 +149,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
     case AV_CODEC_ID_BINKVIDEO:   maxpixels  /= 32;    break;
     case AV_CODEC_ID_CFHD:        maxpixels  /= 128;   break;
     case AV_CODEC_ID_DIRAC:       maxpixels  /= 8192;  break;
-    case AV_CODEC_ID_DST:         maxsamples /= 8192;  break;
+    case AV_CODEC_ID_DST:         maxsamples /= 1<<20; break;
     case AV_CODEC_ID_DXV:         maxpixels  /= 32;    break;
     case AV_CODEC_ID_FFWAVESYNTH: maxsamples /= 16384; break;
     case AV_CODEC_ID_G2M:         maxpixels  /= 64;    break;