avcodec/aac/aacdec: use correct index in deallocation

Fixes: memleak
Fixes: 71084/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_AAC_LATM_fuzzer-5857751899635712

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

libavcodec/aac/aacdec.c

@@ -1104,7 +1104,7 @@ static av_cold int decode_close(AVCodecContext *avctx)
         OutputConfiguration *oc = &ac->oc[i];
         AACUSACConfig *usac = &oc->usac;
         for (int j = 0; j < usac->nb_elems; j++) {
-            AACUsacElemConfig *ec = &usac->elems[i];
+            AACUsacElemConfig *ec = &usac->elems[j];
             av_freep(&ec->ext.pl_data);
         }
     }