blk-stat: convert struct blk_stat_callback to kernel-doc

Most of struct blk_stat_callback documentation is already in kernel-doc
format. Convert the remaining struct members to kernel-doc to avoid
kernel-doc warnings:

Warning: block/blk-stat.h:62 struct member 'list' not described
 in 'blk_stat_callback'
Warning: block/blk-stat.h:62 struct member 'timer_fn' not described
 in 'blk_stat_callback'
Warning: block/blk-stat.h:62 struct member 'rcu' not described
 in 'blk_stat_callback'
Warning: block/blk-stat.h:133 No description found for return value of
 'blk_stat_is_active'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: rddunlap

block/blk-stat.h

@@ -17,7 +17,7 @@
  * timer fires, @cpu_stat is flushed to @stat and @timer_fn is invoked.
  */
 struct blk_stat_callback {
-	/*
+	/**
 	 * @list: RCU list of callbacks for a &struct request_queue.
 	 */
 	struct list_head list;
@@ -50,7 +50,7 @@ struct blk_stat_callback {
 	struct blk_rq_stat *stat;
 
 	/**
-	 * @fn: Callback function.
+	 * @timer_fn: Callback function.
 	 */
 	void (*timer_fn)(struct blk_stat_callback *);
 
@@ -59,6 +59,9 @@ struct blk_stat_callback {
 	 */
 	void *data;
 
+	/**
+	 * @rcu: rcu list head
+	 */
 	struct rcu_head rcu;
 };
 
@@ -126,6 +129,8 @@ void blk_stat_free_callback(struct blk_stat_callback *cb);
  * blk_stat_is_active() - Check if a block statistics callback is currently
  * gathering statistics.
  * @cb: The callback.
+ *
+ * Returns: %true iff the callback is active.
  */
 static inline bool blk_stat_is_active(struct blk_stat_callback *cb)
 {