Use ethosu namespace for core interface

Change-Id: I832b8d7b502ae501e39f1a795d4192506d47fa55
diff --git a/applications/message_process/src/message_process.cpp b/applications/message_process/src/message_process.cpp
index 84a3742..9fa1dbe 100644
--- a/applications/message_process/src/message_process.cpp
+++ b/applications/message_process/src/message_process.cpp
@@ -27,6 +27,7 @@
 
 using namespace std;
 using namespace InferenceProcess;
+using namespace EthosU;
 
 namespace MessageProcess {