sim: Schedule the global sync event at curTick() + simQuantum

The global synchronization event used to be scheduled at
simQuantum. This prevented repeated entries into gem5 from Python as
it can be scheduled in the past. This changeset ensures that the first
global synchronization happens at curTick() + simQuantum instead.

src/sim/simulate.cc

@@ -114,7 +114,7 @@ simulate(Tick num_cycles)
             fatal("Quantum for multi-eventq simulation not specified");
         }
 
-        quantum_event = new GlobalSyncEvent(simQuantum, simQuantum,
+        quantum_event = new GlobalSyncEvent(curTick() + simQuantum, simQuantum,
                             EventBase::Progress_Event_Pri, 0);
 
         inParallelMode = true;