meson,configure: always define UDEV

Signed-off-by: Eric Engestrom <eric.engestrom@imgtec.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
diff --git a/meson.build b/meson.build
index 826cd91..b90127a 100644
--- a/meson.build
+++ b/meson.build
@@ -165,9 +165,9 @@
   with_libkms = _libkms == 'true' or ['linux', 'freebsd', 'dragonfly'].contains(host_machine.system())
 endif
 
+config.set10('UDEV', with_udev)
 if with_udev
   dep_udev = dependency('udev')
-  config.set10('UDEV', true)
 else
   dep_udev = []
 endif