Ruby: Remove assert in RubyPort retry list logic

Remove the assert when adding a port to the RubyPort retry list.
Instead of asserting, just ignore the added port, since it's
already on the list.
Without this patch, Ruby+detailed fails for even the simplest tests

src/mem/ruby/system/RubyPort.hh

@@ -188,8 +188,8 @@ class RubyPort : public MemObject
   private:
     void addToRetryList(MemSlavePort * port)
     {
-        assert(std::find(retryList.begin(), retryList.end(), port) ==
-               retryList.end());
+        if (std::find(retryList.begin(), retryList.end(), port) !=
+               retryList.end()) return;
         retryList.push_back(port);
     }