libaudiohal: Add default values for default port IDs

In aosp/2420554, DeviceHalAidl::mDefault{Input|Output}PortId
fields were missing construction time initializers,
potentially allowing for reading of uninitialized values.

Bug: 205884982
Test: m
Change-Id: I146621a75af53c7973b8978a3c50585b5c1aedda