image: Clarify argument to WriteManifest is config

When creating a model the config layer is appended to the list of
layers and then the last layer is used as the config when writing the
manifest. This change directly uses the config layer to write the
manifest. There is no behavior change but it is less error prone.

server/images.go

@@ -625,12 +625,12 @@ func CreateModel(ctx context.Context, name model.Name, modelFileDir, quantizatio
 		return err
 	}
 
-	layer, err := NewLayer(&b, "application/vnd.docker.container.image.v1+json")
+	configLayer, err := NewLayer(&b, "application/vnd.docker.container.image.v1+json")
 	if err != nil {
 		return err
 	}
 
-	for _, layer := range append(layers, layer) {
+	for _, layer := range append(layers, configLayer) {
 		if layer.status != "" {
 			fn(api.ProgressResponse{Status: layer.status})
 		}
@@ -639,7 +639,7 @@ func CreateModel(ctx context.Context, name model.Name, modelFileDir, quantizatio
 	old, _ := ParseNamedManifest(name)
 
 	fn(api.ProgressResponse{Status: "writing manifest"})
-	if err := WriteManifest(name, layer, layers); err != nil {
+	if err := WriteManifest(name, configLayer, layers); err != nil {
 		return err
 	}