Fix 'Hearing aids' of Accessibility page didn't display connected info promptly when mobile restart

Root Cause: get empty result in hearingAidProfile.getConnectedDevices()

Solution: Need to listen to onServiceConnected() to wait for HearingAidService get connected

Bug: 243489972
Test: make RunSettingsRoboTests ROBOTEST_FILTER=AccessibilityHearingAidPreferenceControllerTest
Change-Id: If6c3b2f3df81388c44e744e364e6258bde8bb645