audio: hal: set mode bt in tfa when entering start_hfp

set mode bt at the start up of start_hfp, in case no sound in spk when ringtone enabled.

Change-Id: I45930d82e376ad47622f1dffc08e80995c128ffc
diff --git a/hal/audio_extn/hfp.c b/hal/audio_extn/hfp.c
index 9306894..2ff7e54 100644
--- a/hal/audio_extn/hfp.c
+++ b/hal/audio_extn/hfp.c
@@ -259,6 +259,8 @@
 
     list_add_tail(&adev->usecase_list, &uc_info->list);
 
+    audio_extn_tfa_98xx_set_mode_bt();
+
     select_devices(adev, hfpmod.ucid);
 
     pcm_dev_rx_id = platform_get_pcm_device_id(uc_info->id, PCM_PLAYBACK);