Change "complexity" key to use public MediaFormat key

Change-Id: I057a51212d512ac4b15d572b53f6606b30b457b2
diff --git a/media/codec2/sfplugin/CCodecConfig.cpp b/media/codec2/sfplugin/CCodecConfig.cpp
index bfd23e3..341ad8b 100644
--- a/media/codec2/sfplugin/CCodecConfig.cpp
+++ b/media/codec2/sfplugin/CCodecConfig.cpp
@@ -924,7 +924,7 @@
         .limitTo(D::ENCODER & (D::CONFIG | D::PARAM)));
     add(ConfigMapper(KEY_FLAC_COMPRESSION_LEVEL, C2_PARAMKEY_COMPLEXITY, "value")
         .limitTo(D::AUDIO & D::ENCODER));
-    add(ConfigMapper("complexity", C2_PARAMKEY_COMPLEXITY, "value")
+    add(ConfigMapper(KEY_COMPLEXITY, C2_PARAMKEY_COMPLEXITY, "value")
         .limitTo(D::ENCODER & (D::CONFIG | D::PARAM)));
 
     add(ConfigMapper(KEY_GRID_COLUMNS, C2_PARAMKEY_TILE_LAYOUT, "columns")