Add associations to sensors

This adds associations to all the sensors on dbus.

Tested: Mapper has lots of sensor associations now.

Change-Id: I9a1c51d6b139e45a228507d29637c29a84b302d9
Signed-off-by: James Feist <james.feist@linux.intel.com>
diff --git a/src/TachSensor.cpp b/src/TachSensor.cpp
index a88c248..c842464 100644
--- a/src/TachSensor.cpp
+++ b/src/TachSensor.cpp
@@ -63,6 +63,9 @@
             "/xyz/openbmc_project/sensors/fan_tach/" + name,
             "xyz.openbmc_project.Sensor.Threshold.Critical");
     }
+    association = objectServer.add_interface(
+        "/xyz/openbmc_project/sensors/fan_tach/" + name,
+        "org.openbmc.Associations");
     setInitialProperties(conn);
     setupPowerMatch(conn);
     setupRead();
@@ -76,6 +79,7 @@
     objServer.remove_interface(thresholdInterfaceWarning);
     objServer.remove_interface(thresholdInterfaceCritical);
     objServer.remove_interface(sensorInterface);
+    objServer.remove_interface(association);
 }
 
 void TachSensor::setupRead(void)