tools/target_enc_fuzzer: A64MULTI5 encoder is very slow, check and adjust threshold

Fixes: Timeout
Fixes: 68999/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_A64MULTI5_fuzzer-5078418784845824

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

tools/target_enc_fuzzer.c

@@ -96,6 +96,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
     maxpixels = maxpixels_per_frame * maxiteration;
     switch (c->p.id) {
     case AV_CODEC_ID_A64_MULTI:         maxpixels  /= 65536;  break;
+    case AV_CODEC_ID_A64_MULTI5:        maxpixels  /= 65536;  break;
     }
 
     maxpixels_per_frame  = FFMIN(maxpixels_per_frame , maxpixels);