nixos/nextcloud: use mkOption.default for datadir

nixos/modules/services/web-apps/nextcloud.nix

@@ -89,7 +89,8 @@ in {
     };
     datadir = mkOption {
       type = types.str;
-      defaultText = "config.services.nextcloud.home";
+      default = config.services.nextcloud.home;
+      defaultText = literalExpression "config.services.nextcloud.home";
       description = ''
         Data storage path of nextcloud.  Will be <xref linkend="opt-services.nextcloud.home" /> by default.
         This folder will be populated with a config.php and data folder which contains the state of the instance (excl the database).";
@@ -629,8 +630,6 @@ in {
           else nextcloud24
         );
 
-      services.nextcloud.datadir = mkOptionDefault config.services.nextcloud.home;
-
       services.nextcloud.phpPackage =
         if versionOlder cfg.package.version "24" then pkgs.php80
         # FIXME: Use PHP 8.1 with Nextcloud 24 and higher, once issues like this one are fixed: