BT: HFP: Set VR flags to false when HS disconnects

When a HS is disconnected while in VR session and then
reconnected again, VR attempt from HS fails as VR flags
mVoiceRecognitionStarted and mWaitingForVoiceRecognition
were not reset to false when HS disconnected.

Change-Id: I008f01393a5529f63cd8392401e1402a9afe70a8