hal: audio: correct ANC headphone path

On msm8998 platform, ANC headphone path is not
enabled correctly. Correct ANC headphone path
mixer controls. Set ANC FB headset backend as
headphones.

Change-Id: I62193c26731f115695cff4386b96917b672eeec6
diff --git a/hal/msm8974/platform.h b/hal/msm8974/platform.h
index 731d81c..0018427 100644
--- a/hal/msm8974/platform.h
+++ b/hal/msm8974/platform.h
@@ -120,6 +120,7 @@
     SND_DEVICE_OUT_VOICE_ANC_HEADSET,
     SND_DEVICE_OUT_VOICE_ANC_FB_HEADSET,
     SND_DEVICE_OUT_SPEAKER_AND_ANC_HEADSET,
+    SND_DEVICE_OUT_SPEAKER_AND_ANC_FB_HEADSET,
     SND_DEVICE_OUT_ANC_HANDSET,
     SND_DEVICE_OUT_SPEAKER_PROTECTED,
     SND_DEVICE_OUT_VOICE_SPEAKER_PROTECTED,