Fix lvalue check in SPIR-V generation

There were several locations in TGlslangToSpvTraverser::handleUserFunctionCall testing for
whether a fn argument should be in the lvalue or rvalue array.  They must get the same
result for indexing sanity, but had slightly different logic.

They're now forced into the same test.

Test/hlsl.opaque-type-bug.frag

@@ -0,0 +1,16 @@
+
+Texture2D      MyTexture : register(t0);
+
+//----------------------------------------------------------------------------------------
+void TexFunc(in const Texture2D t2D, out float3 RGB)
+{    
+    RGB = 0;
+}
+
+//-----------------------------------------------------------------------------------
+void main() 
+{
+    float3 final_RGB;
+
+    TexFunc(MyTexture, final_RGB);
+}