Fix BatteryStatsHistoryTest for low ram devices

The test testStartNextFile() fails on low ram devices as the
default max number of files are different. This change initializes
the constants to a common value for consistency

Test: atest BatteryStatsHistoryTest

Change-Id: I6e34edb4a3b4bd02360621dfe6f202ee061c69f7
(cherry picked from commit bb61a3eed53cdd4ec53ed863b97132c0edfc3477)