Fix shaders with mixed PBK and SSY addresses on the stack (#2329)

* Fix shaders with mixed PBK and SSY addresses on the stack

* Address PR feedback and nits

Ryujinx.Graphics.Shader/Translation/Optimizations/Optimizer.cs

@@ -1,5 +1,4 @@
 using Ryujinx.Graphics.Shader.IntermediateRepresentation;
-using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;