[le audio] notify source added with broadcast source id

In current code, a fake id 0 is used in onSourceAdded callback.
This will cause the App get incorrect source id which will be used to
remove the source later.
Fix is to use the source id from receiver state.

Tag: #bug
Bug: 286890282
Test: atest BassClientServiceTest
Change-Id: I763a51ffafb7f9818697067671eebbb698b40b3b