AudioService: fix NPE in AudioDeviceBroker.setCommunicationRouteForClient

Commit 19a459b7 added code that should only be executed upon selection
of a valid LE device for communication and not when resetting the
device.

Bug: 295288081
Test: place a call and select/unselect a BT LE audio device
Change-Id: I8c560004a6c87b5b33ab9c862b1e4fde2075bb31