privacy: Actually set the blacklist preference

The preference was not being set, which caused this code to throw an NPE on
devices without telephony when opening the privacy preferences.

This bug also affects devices with telephony in that the preference doesn't
update its text. I also got rid of the null check because the preference
always exists, the null check is pointless and ended up hiding this bug.

Change-Id: I95555d44349700a8f29a71a2f2ee9aedf419b49b