Add missing Markdown code span.

This was found using the Clippy `doc_markdown` lint, which we may want
to enable.

Fixes: dd09538fb409 ("rust: alloc: implement `Cmalloc` in module allocator_test")
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 rust/kernel/alloc/allocator_test.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/rust/kernel/alloc/allocator_test.rs b/rust/kernel/alloc/allocator_test.rs
index e3240d16040b..039cd1e36c21 100644
--- a/rust/kernel/alloc/allocator_test.rs
+++ b/rust/kernel/alloc/allocator_test.rs
@@ -4,7 +4,7 @@
 //! of those types (e.g. `CString`) use kernel allocators for instantiation.
 //!
 //! In order to allow userspace test cases to make use of such types as well, implement the
-//! `Cmalloc` allocator within the allocator_test module and type alias all kernel allocators to
+//! `Cmalloc` allocator within the `allocator_test` module and type alias all kernel allocators to
 //! `Cmalloc`. The `Cmalloc` allocator uses libc's `realloc()` function as allocator backend.
 
 #![allow(missing_docs)]
-- 
2.49.0