hal: enable setting gain in case of combo device

In case when speaker-headset combo device is selected, speaker
gain can be set seperatly.

Bug: 22672929
Change-Id: I06c1073b1a6ce238d6f824c6b9a8269e0fc465ab
diff --git a/hal/msm8960/platform.c b/hal/msm8960/platform.c
index 06663a4..c75efbe 100644
--- a/hal/msm8960/platform.c
+++ b/hal/msm8960/platform.c
@@ -547,6 +547,11 @@
     return ret;
 }
 
+void platform_set_speaker_gain_in_combo(struct audio_device *adev __unused,
+                                        snd_device_t snd_device,
+                                        bool enable __unused) {
+}
+
 int platform_set_voice_volume(void *platform, int volume)
 {
     struct platform_data *my_data = (struct platform_data *)platform;