avrcp/device: Fix nullptr dereference on floss

Player settings commands and notification will only be available if the user
initializes AVRCP service with implementation of Player Settings
Interface as it is currently done in JNI layer.

Test: atest AvrcpDeviceTest
Test: manual running floss tests
Bug: 279194432
Change-Id: Idec5b73cf58b367d3c8084f7ffd34c0dc6d51eea