Add missing Markdown code spans.

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

Fixes: b6a006e21b82 ("rust: alloc: introduce allocation flags")
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 rust/kernel/alloc.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/alloc.rs b/rust/kernel/alloc.rs
index fc9c9c41cd79..a2c49e5494d3 100644
--- a/rust/kernel/alloc.rs
+++ b/rust/kernel/alloc.rs
@@ -94,10 +94,10 @@ pub mod flags {
     ///
     /// A lower watermark is applied to allow access to "atomic reserves". The current
     /// implementation doesn't support NMI and few other strict non-preemptive contexts (e.g.
-    /// raw_spin_lock). The same applies to [`GFP_NOWAIT`].
+    /// `raw_spin_lock`). The same applies to [`GFP_NOWAIT`].
     pub const GFP_ATOMIC: Flags = Flags(bindings::GFP_ATOMIC);
 
-    /// Typical for kernel-internal allocations. The caller requires ZONE_NORMAL or a lower zone
+    /// Typical for kernel-internal allocations. The caller requires `ZONE_NORMAL` or a lower zone
     /// for direct access but can direct reclaim.
     pub const GFP_KERNEL: Flags = Flags(bindings::GFP_KERNEL);
 
-- 
2.49.0