Fix flaky BstatsCpuTimesValidationTest test

The change only affects the explicit reset flow, which
is performed at the start of each test method in this test.

Bug: 405208819
Test: atest --rerun-until-failure 100 PowerStatsTests
Flag: EXEMPT bugfix
Change-Id: I16997f969460dba8541a3d3ae75745473deda1af