meson: Fix devkit build when subproject

Where Meson catches us trying to use a file outside the subproject.

meson.build

@@ -561,7 +561,7 @@ if get_option('devkits').length() != 0
   if get_option('default_library') != 'static'
     error('Devkits can only be generated from static libraries')
   endif
-  mkdevkit = [python, files(releng / 'mkdevkit.py')]
+  mkdevkit = [python, releng / 'mkdevkit.py']
   uninstalled_dir = meson.global_build_root() / 'meson-uninstalled'
   devkit_options = [
     '--cc', '>>>', cc.cmd_array(), '<<<',