Replace hci_conn_put with hci_conn_drop

Replace hci_conn_put with hci_conn_drop to remove struct hic_conn from
struct hci_conn_hash.

Reported-by: syzbot+305a91e025a73e4fd6ce@syzkaller.appspotmail.com

net/bluetooth/hci_conn.c

@@ -1716,8 +1716,7 @@ void hci_chan_del(struct hci_chan *chan)
 	/* Prevent new hci_chan's to be created for this hci_conn */
 	set_bit(HCI_CONN_DROP, &conn->flags);
 
-	hci_conn_put(conn);
-
+	hci_conn_drop(conn);
 	skb_queue_purge(&chan->data_q);
 	kfree(chan);
 }