Camera: Clear identity before access device policy manager

When cameraserver query device policy via CameraServiceProxy, the proxy
service uses identity of cameraserver. It causes SecurityException and
does not properly returns the actual query result.

Bug: 290329527
Test: Manual test with TestDPC
Change-Id: Ia02aab3276850c16a14b70c027bd03a17a601b8d
1 file changed