rcu: Docbook for rcu_head_init() and rcu_head_after_call_rcu()

This commit adds the missing asterisks required to make Sphinx pick up
the current header comments for these two functions.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

include/linux/rcupdate.h

@@ -859,7 +859,7 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
 
 /* Has the specified rcu_head structure been handed to call_rcu()? */
 
-/*
+/**
  * rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu()
  * @rhp: The rcu_head structure to initialize.
  *
@@ -874,10 +874,10 @@ static inline void rcu_head_init(struct rcu_head *rhp)
 	rhp->func = (rcu_callback_t)~0L;
 }
 
-/*
+/**
  * rcu_head_after_call_rcu - Has this rcu_head been passed to call_rcu()?
  * @rhp: The rcu_head structure to test.
- * @func: The function passed to call_rcu() along with @rhp.
+ * @f: The function passed to call_rcu() along with @rhp.
  *
  * Returns @true if the @rhp has been passed to call_rcu() with @func,
  * and @false otherwise.  Emits a warning in any other case, including