cpu-simple: Fix BaseSimpleCPU to reset group stats

BaseSimpleCPU::resetStats() should call Stats::Group::resetStats()
to reset new style hierarchy stats.

Change-Id: I932280449b29577d214db56ac8347aca4143c949
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/32434
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/cpu/simple/base.cc

@@ -396,6 +396,7 @@ BaseSimpleCPU::regStats()
 void
 BaseSimpleCPU::resetStats()
 {
+    BaseCPU::resetStats();
     for (auto &thread_info : threadInfo) {
         thread_info->notIdleFraction = (_status != Idle);
     }