Set default color mode to trigger update

Start with invalid color mode so that we are sure
to call downstream for any setColorMode.

Test: manually verify display is in sRGB mode
Change-Id: Iaf511fac1e4cd8acef149528877188708c96856f
diff --git a/services/surfaceflinger/DisplayDevice.cpp b/services/surfaceflinger/DisplayDevice.cpp
index 9af4402..11df4e2 100644
--- a/services/surfaceflinger/DisplayDevice.cpp
+++ b/services/surfaceflinger/DisplayDevice.cpp
@@ -118,6 +118,9 @@
     mNativeWindow = surface = new Surface(producer, false);
     ANativeWindow* const window = mNativeWindow.get();
 
+#ifdef USE_HWC2
+    mActiveColorMode = static_cast<android_color_mode_t>(-1);
+#endif
     /*
      * Create our display's surface
      */