[LeAudioBroadcast] avoid the system register mBroadcastCallback again

There is a "java.lang.IllegalArgumentException: This callback has
already been registered". The system did not disconnect and notifiy
service connect, and it caused the system register the callback again.

Bug: 238374344
Bug: 234312198
Test: build pass.
Change-Id: Iaec1d9d9458add983f3a06f5c30414bce3ce5be5
1 file changed