gnu: extra-cmake-modules: Add proper 'version'.

Fixes a regression introduced in
d26e2b9f.

* gnu/packages/kde-frameworks.scm (extra-cmake-modules)[version]: Set to
"5.21.0".

gnu/packages/kde-frameworks.scm

@@ -30,7 +30,7 @@ (define-module (gnu packages kde-frameworks)
 (define-public extra-cmake-modules
   (package
     (name "extra-cmake-modules")
-    (version kde-frameworks-version)
+    (version "5.21.0")
     (source
       (origin
         (method url-fetch)