Fix Mobile renderer shader instance uniform access

servers/rendering/renderer_rd/forward_mobile/scene_shader_forward_mobile.cpp

@@ -621,7 +621,7 @@ void SceneShaderForwardMobile::init(const String p_defines) {
 		actions.default_filter = ShaderLanguage::FILTER_LINEAR_MIPMAP;
 		actions.default_repeat = ShaderLanguage::REPEAT_ENABLE;
 		actions.global_buffer_array_variable = "global_shader_uniforms.data";
-		actions.instance_uniform_index_variable = "instances.data[instance_index].instance_uniforms_ofs";
+		actions.instance_uniform_index_variable = "instances.data[draw_call.instance_index].instance_uniforms_ofs";
 
 		actions.apply_luminance_multiplier = true; // apply luminance multiplier to screen texture
 		actions.check_multiview_samplers = RendererCompositorRD::get_singleton()->is_xr_enabled(); // Make sure we check sampling multiview textures.