[Chipbar] Only request a11y focus if the chipbar has a button.

Any time the chipbar's content description updates, there will be an
a11y announcement, but the view won't get focus.

Fixes: 260941580
Test: display active unlock chip -> verify chip text is announced but
view isn't focused
Test: display ttt chip that isn't succeeded -> verify chip text is
announced but view isn't focused
Test: display ttt success chip -> verify chip view gets focus (and is
announces)
Test: atest ChipbarCoordinatorTest

Change-Id: I28a29966868611d98d40edbd3d59b1073856e0b4