Allow changing theme to Holo.Light without crashing

Themes that attempt to change the settings theme's parent to
Holo.Light will end up crashing wifi settings.

Themers should override Theme.Settings.Base and leave Theme.Settings.Holo
alone.  Attempting to theme Theme.Settings.Holo will result in crashes
when accessing wifi settings.

This was patch was adapted from
https://github.com/tung91/android_packages_apps_Settings/commit/007f03b559c6d13115c63c4f601ebc4b9324d32d

Change-Id: I61951b892acac6304d2c3dd02668eb70af93eef9