managers: Fix incorrect property name for "Class"

The commit 711ac7a9 introduces a bug in redfish-core/lib/managers.hpp
that it uses the incorrect property name when getting "Class"'s value.

This results in HW CI error that is related to /redfish/v1/Managers/bmc,
and manually access this URI results in 500 InternalError.

Tested: Verify the /redfish/v1/Managers/bmc URI is OK and the HW CI
        passes.

Signed-off-by: Lei YU <yulei.sh@bytedance.com>
Change-Id: Ieb8f98b6cfee6aa22a0320d2410a9b96c536c080
diff --git a/redfish-core/lib/managers.hpp b/redfish-core/lib/managers.hpp
index 201f2f4..d450544 100644
--- a/redfish-core/lib/managers.hpp
+++ b/redfish-core/lib/managers.hpp
@@ -363,7 +363,7 @@
                                          dbus::utility::DbusVariantType>&
                              propPair : intfPair.second)
                     {
-                        if (intfPair.first == "Class")
+                        if (propPair.first == "Class")
                         {
                             classPtr =
                                 std::get_if<std::string>(&propPair.second);