Settings: reset root option selection as necessary

When root is disabled and trying to enable root, a warning dialog pops
up. If the user selects cancel, we need to reset the property to the
actual selection since it hasn't changed.

Change-Id: I6fa1564d86b8473090bbad1b65544481528f0946
Signed-off-by: Roman Birg <roman@cyngn.com>