AudioDeviceInventory: fix devices role management

AudioDeviceInventory.setDevicesRole() implementation was wrong when
trying to merge devices selection for a given <role|strategy> and also
systematically clearing an existing selection before applying a new one.
setDevicesRoles() is used only for non additive scenario where a set of
devices will replace the existing one if any.
If the desired behavior is to add devices to an existing preference,
then addDevicesRole() should be used.

This causes the unwanted systematic reset of call route to default
when switching from one route to another.

Bug: 307161477
Test: repro steps in the bug
Test: AudioCommunicationDeviceTest
Change-Id: I09dd9a6c4ad2425b2d9a281e17f112789baeef17