Fix instance uniform shader crash in custom functions

servers/rendering/renderer_rd/forward_clustered/scene_shader_forward_clustered.cpp

@@ -748,7 +748,7 @@ void SceneShaderForwardClustered::init(RendererStorageRD *p_storage, const Strin
 		actions.default_filter = ShaderLanguage::FILTER_LINEAR_MIPMAP;
 		actions.default_repeat = ShaderLanguage::REPEAT_ENABLE;
 		actions.global_buffer_array_variable = "global_variables.data";
-		actions.instance_uniform_index_variable = "instances.data[instance_index].instance_uniforms_ofs";
+		actions.instance_uniform_index_variable = "instances.data[instance_index_interp].instance_uniforms_ofs";
 
 		compiler.initialize(actions);
 	}