Fix a trivial spelling error in the `rust/kernel/str.rs` file. Fixes: 247b365dc8dc ("rust: add `kernel` crate") Reported-by: Miguel Ojeda <ojeda@kernel.org> Link: https://github.com/Rust-for-Linux/linux/issues/978 Signed-off-by: Patrick Blass <patrickblass@mailbox.org> Reviewed-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com> [Reworded slightly] Signed-off-by: Miguel Ojeda <ojeda@kernel.org>