plasma5Packages.kscreenlocker: depend on wayland-scanner

Otherwise, wayland-scanner would be picked up from the wayland in
buildInputs, which isn't cross-friendly and will stop working when we
split wayland-scanner into a separate package.

pkgs/desktops/plasma-5/kscreenlocker.nix

@@ -1,6 +1,7 @@
 { mkDerivation
 , extra-cmake-modules
 , kdoctools
+, wayland-scanner
 , kcmutils
 , kcrash
 , kdeclarative
@@ -19,7 +20,7 @@
 
 mkDerivation {
   pname = "kscreenlocker";
-  nativeBuildInputs = [ extra-cmake-modules kdoctools ];
+  nativeBuildInputs = [ extra-cmake-modules kdoctools wayland-scanner ];
   buildInputs = [
     kcmutils
     kcrash