rust: bits: disable double_parens check

It is showing in the output of the bits! macro when using the nightly
toolchain, though it's not clear if it is intentional or a bug.
Shut it up for now.

Link: https://github.com/rust-lang/rust-clippy/issues/15852
Reported-by: Richard Henderson <richard.henderson@linaro.org>
Suggested-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Link: https://lore.kernel.org/r/20251010145756.787800-1-pbonzini@redhat.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

rust/qemu-macros/src/lib.rs

@@ -401,7 +401,14 @@ pub fn bits_const_internal(ts: TokenStream) -> TokenStream {
     let ts = proc_macro2::TokenStream::from(ts);
     let mut it = ts.into_iter();
 
-    BitsConstInternal::parse(&mut it)
-        .unwrap_or_else(syn::Error::into_compile_error)
-        .into()
+    let out = BitsConstInternal::parse(&mut it).unwrap_or_else(syn::Error::into_compile_error);
+
+    // https://github.com/rust-lang/rust-clippy/issues/15852
+    quote! {
+        {
+            #[allow(clippy::double_parens)]
+            #out
+        }
+    }
+    .into()
 }