Follow-up I39c2c88d: Always return 'this' in setLevel
Follow-up I39c2c88d: Always return 'this' in setLevel

As the method is supposed to be chainable.

Bug: T296766
Change-Id: Ibb53bd99fbfd9936a99fdec08f224d85b1e0ba24

wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui