audio: Remove unused var 'update_mixer'

Remove update_mixer (as its unused) and change function
signatures wherever used.

Change-Id: I465ddc4bfeba714a7f0d14a7e319a3d1ddc62dbb
CRs-Fixed: 581453
diff --git a/hal/audio_hw.h b/hal/audio_hw.h
index e1172ef..e6ec012 100644
--- a/hal/audio_hw.h
+++ b/hal/audio_hw.h
@@ -242,17 +242,15 @@
 int select_devices(struct audio_device *adev,
                           audio_usecase_t uc_id);
 int disable_audio_route(struct audio_device *adev,
-                               struct audio_usecase *usecase,
-                               bool update_mixer);
+                        struct audio_usecase *usecase);
 int disable_snd_device(struct audio_device *adev,
-                              snd_device_t snd_device,
-                              bool update_mixer);
+                       snd_device_t snd_device);
 int enable_snd_device(struct audio_device *adev,
-                             snd_device_t snd_device,
-                             bool update_mixer);
+                      snd_device_t snd_device);
+
 int enable_audio_route(struct audio_device *adev,
-                              struct audio_usecase *usecase,
-                              bool update_mixer);
+                       struct audio_usecase *usecase);
+
 struct audio_usecase *get_usecase_from_list(struct audio_device *adev,
                                                    audio_usecase_t uc_id);