fix output nFilledLen when prepareForAdaptivePlayback is true

Bug:63560919
Bug:62894603

Change-Id: If1fbd17ebc63743f88c3cbaf2b47a6ee726e06e8
diff --git a/media/libstagefright/codecs/mpeg2dec/SoftMPEG2.cpp b/media/libstagefright/codecs/mpeg2dec/SoftMPEG2.cpp
index 9a69226..9d5f342 100644
--- a/media/libstagefright/codecs/mpeg2dec/SoftMPEG2.cpp
+++ b/media/libstagefright/codecs/mpeg2dec/SoftMPEG2.cpp
@@ -789,7 +789,7 @@
 
             if (s_dec_op.u4_output_present) {
                 ssize_t timeStampIdx;
-                outHeader->nFilledLen = (mWidth * mHeight * 3) / 2;
+                outHeader->nFilledLen = (outputBufferWidth() * outputBufferHeight() * 3) / 2;
 
                 timeStampIdx = getMinTimestampIdx(mTimeStamps, mTimeStampsValid);
                 if (timeStampIdx < 0) {