Fix setTorchMode support for the old HAL version

CameraHardwareInterfaceFlashControl class calls disconnectCameraDevice
when torch is disabled. This closes connection to the camera module,
but mDevice instance is kept and variable is non-NULL which will
prevent connection next time torch is going to be enabled.

Change-Id: Icb1ffb07f05256afd92821f0f4908cda5332c05b