tools/target_dec_fuzzer: Adjust threshold for speex

Fixes: Timeout
Fixes: 59731/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SPEEX_fuzzer-4809436670328832

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 fe167bae96)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

tools/target_dec_fuzzer.c

@@ -274,6 +274,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
     case AV_CODEC_ID_SCPR:        maxpixels  /= 32;    break;
     case AV_CODEC_ID_SCREENPRESSO:maxpixels  /= 64;    break;
     case AV_CODEC_ID_SIMBIOSIS_IMX:maxpixels /= 16384; break;
+    case AV_CODEC_ID_SPEEX:       maxsamples /= 128;   break;
     case AV_CODEC_ID_SMACKAUDIO:  maxsamples /= 4096;  break;
     case AV_CODEC_ID_SMACKVIDEO:  maxpixels  /= 64;    break;
     case AV_CODEC_ID_SNOW:        maxpixels  /= 128;   break;