Fix the bug in HFP API
Fix the bug in HFP API

If we call bluetooth_telephony_audio_open API in next step 6,
the API call fails.

bluetooth-audio.c: bt_ag_open_sco(259) > ALREADY_DONE(0xffff8103)

1. bt_audio_initialize();
2. bt_ag_open_sco();
3. bt_ag_close_sco();
4. bt_audio_deinitialize();
5. bt_audio_initialize();
6. bt_ag_open_sco();

The cause was the headset state was not initailized.
(Because telephony library could not get the event
 - bt_audio_deinitailize also remove the event handler)

Change-Id: Ia724205e394dda8ee956805e951fb40385e623d2

Tizen-Sunfish/bluetooth-frwk,Tizen-Sunfish/bluetooth-frwk