VideoBackends / VideoCommon: add new uniform buffer object for custom shader materials (slot 3, geometry shader buffer moves to slot 4 if available)

Source/Core/VideoCommon/GeometryShaderGen.cpp

@@ -93,7 +93,7 @@ ShaderCode GenerateGeometryShaderCode(APIType api_type, const ShaderHostConfig&
 
   // uniforms
   if (api_type == APIType::OpenGL || api_type == APIType::Vulkan)
-    out.Write("UBO_BINDING(std140, 3) uniform GSBlock {{\n");
+    out.Write("UBO_BINDING(std140, 4) uniform GSBlock {{\n");
   else
     out.Write("cbuffer GSBlock {{\n");