Audio: Device 0 should never be set to HAL

In the scenario of connect A2DP device while muisc is playing, device 0 and force 1
will be used when call setOutputDevice(). This is caused by that setForceUse() and
stopOutput() are called in different thread context separately. According to original
code logic, device 0 will be set to primary audio HAL and take effect. After A2DP is
disconnected, device 0 will be used as output device by primary audio output. Then no
sound any more, as 0 is a undefined value for audio device.

Undefined value doesn't make sence and behavior is unknown if it is set to audio HAL.
And at the same time, after read following original code comments, the original code
logic should be one typo. At least, code logic is totall different with its comments.
Paste the comments here for reference,
         // Do not change the routing if:
         //  - the requested device is 0
         //  - the requested device is the same as current device and force is not specified.
         // Doing this check here allows the caller to call setOutputDevice() without conditions
With this patch, the logic will follow comments totally.

Change-Id: I33560acb8ee7b5263b45db5c94fd282f38797f87