IVGCVSW-2725 Fix issue with ExecuteNetwork and Guid's

Change-Id: I499b2ac3b51390fd725ea8afa64efc7e007be199
Signed-off-by: Saoirse Stewart <saoirse.stewart@arm.com>
diff --git a/src/armnnSerializer/Serializer.cpp b/src/armnnSerializer/Serializer.cpp
index f475be1..d6a23cc 100644
--- a/src/armnnSerializer/Serializer.cpp
+++ b/src/armnnSerializer/Serializer.cpp
@@ -36,7 +36,7 @@
         m_guidMap.insert(guidPair);
         return m_layerId;
     }
-    return m_layerId;
+    return m_guidMap[guid];
 }
 
 // Build FlatBuffer for Input Layer