Add missing const in update service

Per cpp core guidelines, this type should be const.

Tested: Code compiles.  Trivial const change.  cppcheck no longer warns
on this line.

Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: I04aae41701ba1203ff4a68f0b06df2459ee7bb2f
diff --git a/redfish-core/lib/update_service.hpp b/redfish-core/lib/update_service.hpp
index 224d48e..faf8948 100644
--- a/redfish-core/lib/update_service.hpp
+++ b/redfish-core/lib/update_service.hpp
@@ -74,7 +74,7 @@
     m.read(objPath, interfacesProperties);
 
     BMCWEB_LOG_DEBUG << "obj path = " << objPath.str;
-    for (auto& interface : interfacesProperties)
+    for (const auto& interface : interfacesProperties)
     {
         BMCWEB_LOG_DEBUG << "interface = " << interface.first;