[usb_rs] Mark Unused Tuple Struct Fields

An upcoming rustc change (rust-lang/rust#118297)
marks unused tuple fields as dead code. Explicitly mark these structs as
allowed to silence the warning/error.

Bug: 319472617
Change-Id: I248861cd1343a2906a1e97f7e4af06115913eb88
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/978876
Reviewed-by: Colin Nelson <colnnelson@google.com>
Fuchsia-Auto-Submit: Gwen Mittertreiner <gmtr@google.com>
Commit-Queue: Auto-Submit <auto-submit@fuchsia-infra.iam.gserviceaccount.com>

src/lib/usb_rs/src/usb_osx/mod.rs

@@ -371,6 +371,9 @@ impl BulkOutEndpoint {
     }
 }
 
+#[allow(unused_tuple_struct_fields)]
 pub struct ControlEndpoint(Arc<InterfaceInterface500>);
+#[allow(unused_tuple_struct_fields)]
 pub struct InterruptEndpoint(Arc<InterfaceInterface500>);
+#[allow(unused_tuple_struct_fields)]
 pub struct IsochronousEndpoint(Arc<InterfaceInterface500>);