Fix inconsistent USB preference screen title

The title of the USB preference screen ("USB Preferences") is
inconsistent in several ways:

1. It doesn't match the title of the preference that launches it
2. No other preference screens say "preferences" in their title, since
   it's redundant
3. It violates the Material text conventions, which prefer to not
   capitalize titles in the UI

This commit changes it to "USB", which fixes all of the inconsistencies
listed above.

Change-Id: I7330a9e4e121d57ee2140ef60aefb4412b1fe728