Fix accounting bug in BatteryStatsImpl.

A line was added to set mLastChargeStepLevel to level every time the
battery level changed when the device was plugged in. However, it was
added right before an if block that checked if mLastChargeStepLevel was
not equal to level, which then meant that the if block would never
execute. Moving the setting line below the if block to fix that and
removing redundant lines.

Bug: 111360323
Test: atest com.android.internal.os.BatteryStatsTests
Test: atest CtsJobSchedulerTestCases
Test: atest CtsBatterySavingTestCases
Change-Id: I36f1b05f8d344b4d2432696acbf370d47a769d03