Make mServiceListener as null before calling onServiceDisconnected

This way, we can prevent an infinite loop made by apps calling
BluetoothAdapter.getProfileProxy() in the onServiceDisconnected.

Tag: #refactor
Bug: 249213217
Test: atest CtsBluetoothTestCases
Change-Id: I7342befd9a8fc69c778d20140558afb148a4232e