[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 <[email protected]>
Fuchsia-Auto-Submit: Gwen Mittertreiner <[email protected]>
Commit-Queue: Auto-Submit <[email protected]>

Author: gmittert

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>);