netrom: Add missing annotation for nr_info_start()

Sparse reports a warning at nr_info_start()
warning: context imbalance in nr_info_start() - wrong count at exit
The root cause is the missing annotation at nr_info_start()
Add the missing __acquires(&nr_list_lock)

Signed-off-by: Jules Irenge <jbi.octave@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/netrom/af_netrom.c

@@ -1230,6 +1230,7 @@ static int nr_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
 #ifdef CONFIG_PROC_FS
 
 static void *nr_info_start(struct seq_file *seq, loff_t *pos)
+	__acquires(&nr_list_lock)
 {
 	spin_lock_bh(&nr_list_lock);
 	return seq_hlist_start_head(&nr_list, *pos);