AdapterService: Return LE_AUDIO Binder for LE_AUDIO_BROADCAST

LE_AUDIO_BROADCAST don't have any associated service and uses
LeAudioService Binder.

This fixes a regression introduced by https://r.android.com/2663955

Bug: 317289823
Fix: 317289823
Flag: EXEMPT, Regression caused by unflagged changed
Test: atest BluetoothLeBroadcastTest
Change-Id: I608d3220bf02b389b5ecc4e1af21ae3ab86a61f1