macros: use matches!() to fix build warning

This is a new feature, and Rust really wants us to use it.

Signed-off-by: Sean Cross <sean@xobs.io>

macros/src/lib.rs

@@ -66,10 +66,7 @@ pub fn xous_main(args: TokenStream, input: TokenStream) -> TokenStream {
         && f.sig.variadic.is_none()
         && match f.sig.output {
             ReturnType::Default => false,
-            ReturnType::Type(_, ref ty) => match **ty {
-                Type::Never(_) => true,
-                _ => false,
-            },
+            ReturnType::Type(_, ref ty) => matches!(**ty, Type::Never(_)),
         };
 
     if !valid_signature {