PSUSensor: create association before init

By creating the association interface before initializing, it sets up
the sensors with the object mapper.

Tested: Verified the same sensors were available on dbus, and now they
showed up under the ObjectMapper as well.

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: I972b3c313e93b68f741d01a53142e75885d292b4
diff --git a/src/PSUSensor.cpp b/src/PSUSensor.cpp
index c5e8e35..bf02692 100644
--- a/src/PSUSensor.cpp
+++ b/src/PSUSensor.cpp
@@ -68,10 +68,10 @@
         thresholdInterfaceCritical = objectServer.add_interface(
             dbusPath, "xyz.openbmc_project.Sensor.Threshold.Critical");
     }
-    setInitialProperties(conn);
-
     association = objectServer.add_interface(dbusPath, association::interface);
 
+    setInitialProperties(conn);
+
     createInventoryAssoc(conn, association, configurationPath);
     setupRead();
 }