libbinder_ndk_sys visibility restriction

not an API, it's used but shouldn't be or isn't needed

Fixes: 255365984
Change-Id: Ia62a2808f89b23ce7bf5b8ed199b0ae5514c60ab
Test: N/A
diff --git a/libs/binder/rust/Android.bp b/libs/binder/rust/Android.bp
index a135796..738d16a 100644
--- a/libs/binder/rust/Android.bp
+++ b/libs/binder/rust/Android.bp
@@ -88,6 +88,7 @@
     min_sdk_version: "Tiramisu",
     lints: "none",
     clippy_lints: "none",
+    visibility: [":__subpackages__"],
 }
 
 rust_bindgen {