Force fixed volume for TTS stream

Always play Transmitted Through Speaker stream at max volume instead
of tracking media stream volume.

Bug: 23729461.
Change-Id: I61021f59617bb851a4cd7da80924e587029e96a3
diff --git a/services/audiopolicy/enginedefault/src/Gains.cpp b/services/audiopolicy/enginedefault/src/Gains.cpp
index 78f2909..d06365c 100644
--- a/services/audiopolicy/enginedefault/src/Gains.cpp
+++ b/services/audiopolicy/enginedefault/src/Gains.cpp
@@ -171,10 +171,10 @@
     },
     { // AUDIO_STREAM_TTS
       // "Transmitted Through Speaker": always silent except on DEVICE_CATEGORY_SPEAKER
-        Gains::sSilentVolumeCurve, // DEVICE_CATEGORY_HEADSET
-        Gains::sLinearVolumeCurve, // DEVICE_CATEGORY_SPEAKER
-        Gains::sSilentVolumeCurve, // DEVICE_CATEGORY_EARPIECE
-        Gains::sSilentVolumeCurve  // DEVICE_CATEGORY_EXT_MEDIA
+        Gains::sSilentVolumeCurve,    // DEVICE_CATEGORY_HEADSET
+        Gains::sFullScaleVolumeCurve, // DEVICE_CATEGORY_SPEAKER
+        Gains::sSilentVolumeCurve,    // DEVICE_CATEGORY_EARPIECE
+        Gains::sSilentVolumeCurve     // DEVICE_CATEGORY_EXT_MEDIA
     },
     { // AUDIO_STREAM_ACCESSIBILITY
         Gains::sDefaultMediaVolumeCurve, // DEVICE_CATEGORY_HEADSET