Bluetooth: ISO: Fix a use-after-free of the hci_conn pointer

Bluetooth: ISO: Fix a use-after-free of the hci_conn pointer

In iso_sock_rebind_bc(), the bis pointer is cached, then the socket lock is
dropped:
	bis = iso_pi(sk)->conn->hcon;
	/* Release the socket before lookups since that requires hci_dev_lock
	 * which shall not be acquired while holding sock_lock for proper
	 * ordering.
	 */
	release_sock(sk);
	hci_dev_lock(bis->hdev);

During the unlocked window, could a concurrent close() destroy the connection
and free the bis structure, causing hci_dev_lock(bis->hdev) to access memory
after it is freed, fix this by using the hdev reference which was safely
acquired via iso_conn_get_hdev().

Fixes: d3413703d5f8 ("Bluetooth: ISO: Add support to bind to trigger PAST")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>