Fix a compile error in label.rs

Because we aren't testing in CI yet, this wasn't caught after I changed
the parent commit to make the fields private.

Change-Id: I56060507411f8e14807852720481a7476a6a6964
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/23580
Commit-Queue: Matt Stark <msta@google.com>
Reviewed-by: Takuto Ikuta <tikuta@google.com>

src/gn/starlark/crates/ffi/src/label.rs

diff --git a/src/gn/starlark/crates/ffi/src/label.rs b/src/gn/starlark/crates/ffi/src/label.rs
index 15a85ad..b1eedf6 100644
--- a/src/gn/starlark/crates/ffi/src/label.rs
+++ b/src/gn/starlark/crates/ffi/src/label.rs
@@ -27,9 +27,6 @@
 
     /// Returns a `LabelRef` referencing the directory and name of this label.
     pub fn as_ref<'a>(&'a self) -> LabelRef<'a> {
-        LabelRef {
-            package: self.package(),
-            name: self.name(),
-        }
+        LabelRef::new(self.package(), self.name())
     }
 }