Make icon size on Printing settings match the rest of settings

Make icon size on Printing settings match the rest of settings

The icons on this page were being displayed at 48dp because we were
using a generic Preference element, instead of the custom settings
AppPreference which we use in lots of other places in settings for
displaying app entries in a list (and has a custom layout that ends up
with 32dp icons).

Fixes: 78654919
Test: manual (go to Settings -> Connected devices -> Connection
preferences -> Printing)

Change-Id: Icf21ab6b41fc00936cd58f3342a8c5502c6dd87f