pixelstats: MM Metrics: Fix offset-by-2 bug

* Fixed the known offset-by-2 bug (previously hot-fixed in dashboard by
  compensating the offset) in the direct reclaim metrics.
    - dashboard data will be fixed later accordingly (reverting the
      offset-compensation).

Bug: 333163458
Test: atest pixelstats_mm_test
      Note: The test results show fewer mismatched data, and confirm
      the fix.
Change-Id: I96fd551ff23ab0df07744a8bcd4204f1de203f69
Signed-off-by: Robin Hsu <robinhsu@google.com>