nixos/storage: Don't put whole config in devspec

While it may be handy to put the whole configuration of the
corresponding device specification into the values of the options
referring to them, this unfortunately blows up the size of the JSON
output we pass to nixpart.

This is unnecessary because we're only interested in the UUID.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>

nixos/modules/tasks/storage/default.nix

@@ -281,7 +281,7 @@ in
         # If no label is set, reference the device via the generated UUID in
         # genericOptions.uuid.
         (lib.mkIf (config.storage != null && config.label == null) {
-          device = "/dev/disk/by-uuid/${config.storage.config.uuid}";
+          device = "/dev/disk/by-uuid/${config.storage.uuid}";
         })
       ];
     }));
@@ -304,7 +304,7 @@ in
       # If no label is set, reference the device via the generated UUID in
       # genericOptions.uuid.
       config = lib.mkIf (config.storage != null && !options.label.isDefined) {
-        device = "/dev/disk/by-uuid/${config.storage.config.uuid}";
+        device = "/dev/disk/by-uuid/${config.storage.uuid}";
       };
     }));
   };

nixos/modules/tasks/storage/lib.nix

@@ -92,10 +92,10 @@ let
   in if typeAndName == null then null else rec {
     type = lib.head typeAndName;
     name = lib.last typeAndName;
-    # The configuration entry for the storage spec. Note that we don't need to
-    # check whether ${type} and ${name} exist, because they're already checked
-    # in assertSpec.
-    config = cfg.${type}.${name};
+    # The generated UUID for the storage spec. Note that we don't need to check
+    # whether ${type} and ${name} exist, because they're already checked in
+    # assertSpec.
+    inherit (cfg.${type}.${name}) uuid;
   };
 
   /* Validate the device specification and return true if it's valid or false if