[openweave] Fix incorrect usage of TSM singleton

The call changed in this commit is invoked on a newly-constructed
ThreadStackManager rather than on the singleton instance. Correcting
this mistake.

Change-Id: I109b8d7e1c111c911518828b6aa859c4fa544ce2
diff --git a/src/adaptations/device-layer/include/Weave/DeviceLayer/internal/GenericConfigurationManagerImpl.ipp b/src/adaptations/device-layer/include/Weave/DeviceLayer/internal/GenericConfigurationManagerImpl.ipp
index 2f2247e..a7efb4f 100644
--- a/src/adaptations/device-layer/include/Weave/DeviceLayer/internal/GenericConfigurationManagerImpl.ipp
+++ b/src/adaptations/device-layer/include/Weave/DeviceLayer/internal/GenericConfigurationManagerImpl.ipp
@@ -223,7 +223,7 @@
 WEAVE_ERROR GenericConfigurationManagerImpl<ImplClass>::_GetPrimary802154MACAddress(uint8_t * buf)
 {
 #if WEAVE_DEVICE_CONFIG_ENABLE_THREAD
-    return ThreadStackManager().GetPrimary802154MACAddress(buf);
+    return ThreadStackMgr().GetPrimary802154MACAddress(buf);
 #else
     return WEAVE_DEVICE_ERROR_CONFIG_NOT_FOUND;
 #endif // WEAVE_DEVICE_CONFIG_ENABLE_THREAD