MAINTAINERS: update atomic infrastructure entry to include Rust

I would like to help review atomic related patches, especially Rust
related ones, hence add myself as an reviewer.

Suggested-by: Boqun Feng <boqun.feng@gmail.com>
Acked-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/r/20250723233312.3304339-6-gary@kernel.org