dbusconfiguration: Fix mapper call

Our downstream version of the cpp mapper allowed an
empty path for GetSubTree, change this to root "/".

Tested-by: Configuration loads with both mappers

Change-Id: I206d2deaf9bb54acda15eccb778633f10398098a
Signed-off-by: James Feist <james.feist@linux.intel.com>
diff --git a/dbus/dbusconfiguration.cpp b/dbus/dbusconfiguration.cpp
index 93f9c1f..ae08cda 100644
--- a/dbus/dbusconfiguration.cpp
+++ b/dbus/dbusconfiguration.cpp
@@ -170,7 +170,7 @@
         bus.new_method_call("xyz.openbmc_project.ObjectMapper",
                             "/xyz/openbmc_project/object_mapper",
                             "xyz.openbmc_project.ObjectMapper", "GetSubTree");
-    mapper.append("", 0,
+    mapper.append("/", 0,
                   std::array<const char*, 6>{objectManagerInterface,
                                              pidConfigurationInterface,
                                              pidZoneConfigurationInterface,