Fix SmartspaceService callback comparison.

We should use binder references when comparing two IPC callbacks.

Test: Inject a test code into LocscreenSmartspaceController#reloadSmartspace() that register and unregister a test smartspace listener. Verify that the listeners is
get invoked without the fix and is not get invoked with the fix.
Change-Id: I3229c6496cde43ba1df65412857eb36b47b525c4