aacenc: fix timestamp off by one frame

Bug: 137245963
Test: manual
Change-Id: I567890f3d04544c12adfe29a6a23c06f1db699e7
diff --git a/media/codec2/components/aac/C2SoftAacEnc.h b/media/codec2/components/aac/C2SoftAacEnc.h
index a38be19..2655039 100644
--- a/media/codec2/components/aac/C2SoftAacEnc.h
+++ b/media/codec2/components/aac/C2SoftAacEnc.h
@@ -56,7 +56,7 @@
     bool mSentCodecSpecificData;
     bool mInputTimeSet;
     size_t mInputSize;
-    c2_cntr64_t mInputTimeUs;
+    c2_cntr64_t mNextFrameTimestampUs;
 
     bool mSignalledError;
     std::atomic_uint64_t mOutIndex;