audio: Check result from oneway calls

As oneway HIDL calls generate methods that return 'Result<void>',
the returned value must be checked to avoid triggering an
assertion if the result was an error (e.g. due to the client death).

Bug: 151900655
Test: N/A
Change-Id: I4721240b5959d6f11cb4447b30928bf4c83da058