Bluetooth: hci_conn: Fix crash on hci_create_cis_sync

When attempting to connect multiple ISO sockets without using
DEFER_SETUP may result in the following crash:

BUG: KASAN: null-ptr-deref in hci_create_cis_sync+0x18b/0x2b0
Read of size 2 at addr 0000000000000036 by task kworker/u3:1/50

CPU: 0 PID: 50 Comm: kworker/u3:1 Not tainted
6.0.0-rc7-02243-gb84a13ff4eda #4373
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009),
BIOS 1.16.0-1.fc36 04/01/2014
Workqueue: hci0 hci_cmd_sync_work
Call Trace:
 <TASK>
 dump_stack_lvl+0x19/0x27
 kasan_report+0xbc/0xf0
 ? hci_create_cis_sync+0x18b/0x2b0
 hci_create_cis_sync+0x18b/0x2b0
 ? get_link_mode+0xd0/0xd0
 ? __ww_mutex_lock_slowpath+0x10/0x10
 ? mutex_lock+0xe0/0xe0
 ? get_link_mode+0xd0/0xd0
 hci_cmd_sync_work+0x111/0x190
 process_one_work+0x427/0x650
 worker_thread+0x87/0x750
 ? process_one_work+0x650/0x650
 kthread+0x14e/0x180
 ? kthread_exit+0x50/0x50
 ret_from_fork+0x22/0x30
 </TASK>

Fixes: 26afbd82 ("Bluetooth: Add initial implementation of CIS connections")
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

net/bluetooth/hci_conn.c

@@ -1879,7 +1879,7 @@ static int hci_create_cis_sync(struct hci_dev *hdev, void *data)
 			continue;
 
 		/* Check if all CIS(s) belonging to a CIG are ready */
-		if (conn->link->state != BT_CONNECTED ||
+		if (!conn->link || conn->link->state != BT_CONNECTED ||
 		    conn->state != BT_CONNECT) {
 			cmd.cp.num_cis = 0;
 			break;