sunrpc: fix missing kernel-doc

Fix missing sunrpc kernel-doc:

Warning(linux-2.6.25-git7//net/sunrpc/xprt.c:451): No description found for parameter 'action'
Signed-off-by: NRandy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sunrpc/xprt.c

@@ -445,7 +445,7 @@ EXPORT_SYMBOL_GPL(xprt_wake_pending_tasks);
 /**
  * xprt_wait_for_buffer_space - wait for transport output buffer to clear
  * @task: task to be put to sleep
- *
+ * @action: function pointer to be executed after wait
  */
 void xprt_wait_for_buffer_space(struct rpc_task *task)
 {