Update strings when shortString is true

After b/64124535, battery strings in settings page use shortString
version. This cl updates the charging string in this situation to
match the mock.

Note that no matter whether we use shorString, the chargingLabel
should remain the same.

Bug: 64752046
Test: RunSettingsRoboTests
Change-Id: I4395d4660e212688cd560ca0b124acbd9c099cc9