Fix unused-parameter warnings

These are exposed when frameworks/av/include is moved from being a
system include directory to a normal include directory.

Test: m -j checkbuild
Change-Id: I0e3787fbee70339f7dcbc979f448800ecfff0f17
diff --git a/include/media/MediaMetadataRetrieverInterface.h b/include/media/MediaMetadataRetrieverInterface.h
index bce6ee3..a5e1350 100644
--- a/include/media/MediaMetadataRetrieverInterface.h
+++ b/include/media/MediaMetadataRetrieverInterface.h
@@ -54,9 +54,9 @@
     MediaMetadataRetrieverInterface() {}
 
     virtual             ~MediaMetadataRetrieverInterface() {}
-    virtual VideoFrame* getFrameAtTime(int64_t timeUs, int option) { return NULL; }
+    virtual VideoFrame* getFrameAtTime(int64_t /*timeUs*/, int /*option*/) { return NULL; }
     virtual MediaAlbumArt* extractAlbumArt() { return NULL; }
-    virtual const char* extractMetadata(int keyCode) { return NULL; }
+    virtual const char* extractMetadata(int /*keyCode*/) { return NULL; }
 };
 
 }; // namespace android