Add missing Markdown code spans and also convert them into intra-doc
links.

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

Fixes: e0020ba6cbcb ("rust: add PidNamespace")
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 rust/kernel/task.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs
index 49012e711942..ca1209b997c4 100644
--- a/rust/kernel/task.rs
+++ b/rust/kernel/task.rs
@@ -156,10 +156,10 @@ fn deref(&self) -> &Self::Target {
         }
     }
 
-    /// Returns a PidNamespace reference for the currently executing task's/thread's pid namespace.
+    /// Returns a [`PidNamespace`] reference for the currently executing task's/thread's pid namespace.
     ///
     /// This function can be used to create an unbounded lifetime by e.g., storing the returned
-    /// PidNamespace in a global variable which would be a bug. So the recommended way to get the
+    /// [`PidNamespace`] in a global variable which would be a bug. So the recommended way to get the
     /// current task's/thread's pid namespace is to use the [`current_pid_ns`] macro because it is
     /// safe.
     ///
-- 
2.49.0