CCodec: flush reorder stash at flush

Bug: 123349335
Test: bug repro steps
Change-Id: I6be571e2ca640b86eb2d227d92492bc8f0466ff5
diff --git a/media/codec2/sfplugin/CCodecBufferChannel.h b/media/codec2/sfplugin/CCodecBufferChannel.h
index fd806b7..ebc1491 100644
--- a/media/codec2/sfplugin/CCodecBufferChannel.h
+++ b/media/codec2/sfplugin/CCodecBufferChannel.h
@@ -359,6 +359,7 @@
         ReorderStash();
 
         void clear();
+        void flush();
         void setDepth(uint32_t depth);
         void setKey(C2Config::ordinal_key_t key);
         bool pop(Entry *entry);