audio: init return code to avoid effect's fault state

Effect command doesn't necessarily fill cmd return code into &cmdStatus,
so we should initialize cmdStatus to avoid uninitialized value propagates
to upper stack caller.

Change-Id: I5694616c9d3d66071241958f54a03b8d3b9d881e

CRs-fixed: 1016867
Conflicts:
	services/audioflinger/Effects.cpp

Change-Id: I5694616c9d3d66071241958f54a03b8d3b9d881e