Google RoT: simplify subtree iteration

Use structured binding declaration to avoid verbose typing of subtree
response.

Tested:
1. code compiles
2. tested on hardware and RoT resources worked as expected.

Signed-off-by: Nan Zhou <nanzhoumails@gmail.com>
Change-Id: I22758c196a097cce8e94208085fd59ce1363cefc
diff --git a/include/google/google_service_root.hpp b/include/google/google_service_root.hpp
index 2d43146..2100fab 100644
--- a/include/google/google_service_root.hpp
+++ b/include/google/google_service_root.hpp
@@ -67,22 +67,18 @@
         redfish::messages::internalError(asyncResp->res);
         return;
     }
-    // Iterate over all retrieved ObjectPaths.
-    for (const std::pair<
-             std::string,
-             std::vector<std::pair<std::string, std::vector<std::string>>>>&
-             object : subtree)
+    for (const auto& [path, services] : subtree)
     {
-        sdbusplus::message::object_path objPath(object.first);
-        if (objPath.filename() != rotId || object.second.empty())
+        sdbusplus::message::object_path objPath(path);
+        if (objPath.filename() != rotId || services.empty())
         {
             continue;
         }
 
         ResolvedEntity resolvedEntity = {
             .id = rotId,
-            .service = object.second[0].first,
-            .object = object.first,
+            .service = services[0].first,
+            .object = path,
             .interface = "xyz.openbmc_project.Control.Hoth"};
         entityHandler(command, asyncResp, resolvedEntity);
         return;