Audio: Fix Visualizer's get/set parameter methods not worked bug

This commit fixes broken Visualizer's get/set parameter methods.
The bug was introduced by modifications to avoid complilation errors.(*1,*2,*3)

(*1) 91b6deea4562bbec7713f6796a6ecff200424832

    frameworks/media: Fix aliasing violations

(*2) 3762008c5fda41501dfb18f218de52fda96281eb

    av: Fix aliasing violations in AudioFlinger

(*3) bf935694368da97e79004b8197a5f6f2e9460c11

    EffectVisualizer: Fix aliasing violations