tools/target_dec_fuzzer: Adjust VP7 threshold

Fixes: Timeout (110sec -> 10sec)
Fixes: 17705/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_VP7_fuzzer-5765834135306240

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

@@ -153,6 +153,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
     case AV_CODEC_ID_MSS2:        maxpixels /= 16384; break;
     case AV_CODEC_ID_SNOW:        maxpixels /= 128; break;
     case AV_CODEC_ID_TRUEMOTION2: maxpixels /= 1024; break;
+    case AV_CODEC_ID_VP7:         maxpixels /= 256;  break;
     }