Settings: fix led pulsespeedoff disable behaviour

Keep led pulsespeedoff disabled if pulsespeedon is
disabled.  This ensures that pulsespeedoff stays
disabled if onOffChangeable was set to false.  Fixes
problem where charged led pulsespeed off looks to
be configurable in the ui and thereby creating user
confusion.

Change-Id: I6ac7f630544bf719b39e1ddcab435322975430c8
Add missing string