EffectDownmix: Fix float mode and enable

Test: Play Music with multichannel source using float and int16 downmixer
Bug: 121222814
Change-Id: If97770991edc3bec02edc82101aaa8ad86ac4bcf
diff --git a/media/libeffects/downmix/Android.bp b/media/libeffects/downmix/Android.bp
index 227f2a1..9c82b1d 100644
--- a/media/libeffects/downmix/Android.bp
+++ b/media/libeffects/downmix/Android.bp
@@ -13,7 +13,7 @@
     relative_install_path: "soundfx",
 
     cflags: [
-        //"-DBUILD_FLOAT",
+        "-DBUILD_FLOAT",
         "-fvisibility=hidden",
         "-Wall",
         "-Werror",