libmix: ignore mSizeChanged flag in flush function to avoid resolution changing issue.

BZ: 5196

The clip's resolution in container and in SPS are different, a DECODE_FORMAT_CHANGE should be returned
from decoder, but the flush() will damage this mechanism through modifing the mSizeChanged flag.
So ignore this flag in flush().

Change-Id: Ia86c2631cb43165a5a52c5c15b0050a30ede205a
Signed-off-by: xli111 <xiaowei.a.li@intel.com>
diff --git a/videodecoder/VideoDecoderBase.cpp b/videodecoder/VideoDecoderBase.cpp
index 912c347..1fc8835 100644
--- a/videodecoder/VideoDecoderBase.cpp
+++ b/videodecoder/VideoDecoderBase.cpp
@@ -157,7 +157,6 @@
     mOutputHead = NULL;
     mOutputTail = NULL;
     mDecodingFrame = false;
-    mSizeChanged = false;
 
     // initialize surface buffer without resetting mapped/raw data
     initSurfaceBuffer(false);