Set active volume device to null if there is no new device

Change broadcastActiveDevice to also set the global active device
variable and move the AVRCP volume memory code to that function in order
to simplify the code.

Fixes: 110162585
Test: Forget device while device is active
Change-Id: If8a66b51a762c5edc5dd5133636f91454c9cab65
2 files changed