Add missing Markdown code span.

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

Fixes: bbe3b4d1580d ("rust: of: add `of::DeviceId` abstraction")
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 rust/kernel/of.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/rust/kernel/of.rs b/rust/kernel/of.rs
index 04f2d8ef29cb..60ed551b50fb 100644
--- a/rust/kernel/of.rs
+++ b/rust/kernel/of.rs
@@ -4,7 +4,7 @@
 
 use crate::{bindings, device_id::RawDeviceId, prelude::*};
 
-/// IdTable type for OF drivers.
+/// `IdTable` type for OF drivers.
 pub type IdTable<T> = &'static dyn kernel::device_id::IdTable<DeviceId, T>;
 
 /// An open firmware device id.
-- 
2.49.0