Bluetooth: ISO: Check socket flag instead of hcon

In the Linux kernel, the following vulnerability has been resolved:

Bluetooth: ISO: Check socket flag instead of hcon

This fixes the following Smatch static checker warning:

net/bluetooth/iso.c:1364 iso_sock_recvmsg()
error: we previously assumed 'pi->conn->hcon' could be null (line 1359)

net/bluetooth/iso.c
1347 static int iso_sock_recvmsg(struct socket *sock, struct msghdr *msg,
1348 size_t len, int flags)
1349 {
1350 struct sock *sk = sock->sk;
1351 struct iso_pinfo *pi = iso_pi(sk);
1352
1353 BT_DBG("sk %p", sk);
1354
1355 if (test_and_clear_bit(BT_SK_DEFER_SETUP,
&bt_sk(sk)->flags)) {
1356 lock_sock(sk);
1357 switch (sk->sk_state) {
1358 case BT_CONNECT2:
1359 if (pi->conn->hcon &&
^^^^^^^^^^^^^^ If ->hcon is NULL

1360 test_bit(HCI_CONN_PA_SYNC,
&pi->conn->hcon->flags)) {
1361 iso_conn_big_sync(sk);
1362 sk->sk_state = BT_LISTEN;
1363 } else {
--> 1364 iso_conn_defer_accept(pi->conn->hcon);
^^^^^^^^^^^^^^
then we're toast

1365 sk->sk_state = BT_…