Fix Icon size in DocumentsUI

For XXHDPI devices if you go into Settings/Display and Notification light and select a custom value (application) you will see a GIANT icon.

Before - http://i.imgur.com/DRkua3T.png

After - http://i.imgur.com/f7xW4tY.png

Change-Id: Ia355bddc515906134c8b3b4e67d381aaacceec78
(cherry picked from commit cc5ae6b426f7a53ba8bdd1726b6e99e1318d50ae)