BatteryStats: explicitly copy the wakeup reasons

As the wakeup reasons received from binder callback are in const
reference, std::move the parameter will result in a copy operation in
order to fulfill the const restriction. Update to reflect this
explicitly.

Test: adb shell dumpsys batterystats --history
Bug: 173165219
Change-Id: I6ab995cc11600b37123651bacc2015a3bf1a4bf6