arch-gcn3, misc: Added missing override to protocol_tester.hh

Clang will return a missing-override error when compiling X86_GCN4
without this change.

Change-Id: Ib5fd9ba5c27ddc15561198bfc90d27b7599a7923
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/37537
Reviewed-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>

src/cpu/testers/gpu_ruby_test/protocol_tester.hh

@@ -117,7 +117,7 @@ class ProtocolTester : public ClockedObject
     typedef AddressManager::Location Location;
     typedef AddressManager::Value Value;
 
-    void init();
+    void init() override;
     RequestorID requestorId() { return _requestorId; };
     Port& getPort(const std::string &if_name,
                   PortID idx=InvalidPortID) override;