Fixed backend id argument parsing in ExecuteNetwork

Change-Id: I99498a633d75a2b4bdcd059627b07beaa9984890
diff --git a/tests/ExecuteNetwork/ExecuteNetwork.cpp b/tests/ExecuteNetwork/ExecuteNetwork.cpp
index 4ebc998..cfddc38 100644
--- a/tests/ExecuteNetwork/ExecuteNetwork.cpp
+++ b/tests/ExecuteNetwork/ExecuteNetwork.cpp
@@ -589,7 +589,8 @@
     else // Run single test
     {
         // Get the preferred order of compute devices.
-        std::vector<armnn::BackendId> computeDevices = vm["compute"].as<std::vector<armnn::BackendId>>();
+        std::vector<std::string> computeDevicesAsStrings = vm["compute"].as<std::vector<std::string>>();
+        std::vector<armnn::BackendId> computeDevices(computeDevicesAsStrings.begin(), computeDevicesAsStrings.end());
 
         // Remove duplicates from the list of compute devices.
         RemoveDuplicateDevices(computeDevices);