Fetch bluetooth cached device name outside synchronized block.

mConnectedDevices is being accessed from both main and background thread
in BluetoothControllerImpl. This is leading to an ANR in cases where the
resource is being used in the background thread, and the main thread
is trying to update it in a synchronized block.

Bug: 323995015
Test: local CPU profiling
Flag: NONE
Change-Id: I72d1a0b61038b29a273c1b712461837e5e065e5e