Bug 1089486 - [NFC] Disable NFC toggle in settings during NFC HW change,  r=arthur.chen, r=gweng

https://bugzilla.mozilla.org/show_bug.cgi?id=1089486
The value of the check box has already been bound to `nfc.enabled` so we should not manipulate the value here. This handler should only update the value of `this._checkboc.disabled`.