Don't use getCurrentState() in BatteryStateMachine

getCurrentState() could throw ArrayIndexOutOfBoundsException
when it's called during state transition.

To avoid exception we can use the last connection state instead.

Bug: 374013809
Flag: EXEMPT, no logic change
Test: atest BatterServiceTest BatteryStateMachineTest

Change-Id: I1cbbb4da6b16873b3f52d7d7c54c281413cde60d