cmake: modules: extensions: fix a section header

The table of contents at the top of the file has 'Devicetree
extensions' as the name of the section containing... those things.

The actual place in the file where they are defined has a different
title, though, defeating searching in the file for that section name.

Fix it.

Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>
1 file changed