rust: error: Markdown style nit

This patch fixes a trivial markdown style nit in the `SAFETY` comment.

Signed-off-by: Manmohan Shukla <manmshuk@gmail.com>
Reviewed-by: Jianguo Bao <roidinev@gmail.com>
Reviewed-by: Finn Behrens <me@kloenk.dev>
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>
Link: https://lore.kernel.org/r/20230906204857.85619-1-manmshuk@gmail.com

rust/kernel/error.rs

@@ -133,7 +133,7 @@ impl Error {
     /// Returns the error encoded as a pointer.
     #[allow(dead_code)]
     pub(crate) fn to_ptr<T>(self) -> *mut T {
-        // SAFETY: self.0 is a valid error due to its invariant.
+        // SAFETY: `self.0` is a valid error due to its invariant.
         unsafe { bindings::ERR_PTR(self.0.into()) as *mut _ }
     }