Bluetooth: Fix NULL pointer dereference in mgmt context

Bluetooth: Fix NULL pointer dereference in mgmt context

Adds missing callback assignment to cmd_complete in pending management command
context. Dump path involves security procedure performed on legacy (pre-SSP)
devices with service security requirements set to HIGH (16digits PIN).
It fails when shorter PIN is delivered by user.

[    1.517950] Bluetooth: PIN code is not 16 bytes long
[    1.518491] BUG: unable to handle kernel NULL pointer dereference at           (null)
[    1.518584] IP: [<          (null)>]           (null)
[    1.518584] PGD 9e08067 PUD 9fdf067 PMD 0
[    1.518584] Oops: 0010 [#1] SMP
[    1.518584] Modules linked in:
[    1.518584] CPU: 0 PID: 1002 Comm: kworker/u3:2 Not tainted 4.8.0-rc6-354649-gaf4168c #16
[    1.518584] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.9.3-20160701_074356-anatol 04/01/2014
[    1.518584] Workqueue: hci0 hci_rx_work
[    1.518584] task: ffff880009ce14c0 task.stack: ffff880009e10000
[    1.518584] RIP: 0010:[<0000000000000000>]  [<          (null)>]           (null)
[    1.518584] RSP: 0018:ffff880009e13bc8  EFLAGS: 00010293
[    1.518584] RAX: 0000000000000000 RBX: ffff880009eed100 RCX: 0000000000000006
[    1.518584] RDX: ffff880009ddc000 RSI: 0000000000000000 RDI: ffff880009eed100
[    1.518584] RBP: ffff880009e13be0 R08: 0000000000000000 R09: 0000000000000001
[    1.518584] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
[    1.518584] R13: ffff880009e13ccd R14: ffff880009ddc000 R15: ffff880009ddc010
[    1.518584] FS:  0000000000000000(0000) GS:ffff88000bc00000(0000) knlGS:0000000000000000
[    1.518584] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    1.518584] CR2: 0000000000000000 CR3: 0000000009fdd000 CR4: 00000000000006f0
[    1.518584] Stack:
[    1.518584]  ffffffff81909808 ffff880009e13cce ffff880009e0d40b ffff880009e13c68
[    1.518584]  ffffffff818f428d 00000000024000c0 ffff880009e13c08 ffffffff810ca903
[    1.518584]  ffff880009e13c48 ffffffff811ade34 ffffffff8178c31f ffff880009ee6200
[    1.518584] Call Trace:
[    1.518584]  [<ffffffff81909808>] ? mgmt_pin_code_neg_reply_complete+0x38/0x60
[    1.518584]  [<ffffffff818f428d>] hci_cmd_complete_evt+0x69d/0x3200
[    1.518584]  [<ffffffff810ca903>] ? rcu_read_lock_sched_held+0x53/0x60
[    1.518584]  [<ffffffff811ade34>] ? kmem_cache_alloc+0x1a4/0x200
[    1.518584]  [<ffffffff8178c31f>] ? skb_clone+0x4f/0xa0
[    1.518584]  [<ffffffff818f9d81>] hci_event_packet+0x8e1/0x28e0
[    1.518584]  [<ffffffff81a421f1>] ? _raw_spin_unlock_irqrestore+0x31/0x50
[    1.518584]  [<ffffffff810aea3e>] ? trace_hardirqs_on_caller+0xee/0x1b0
[    1.518584]  [<ffffffff818e6bd1>] hci_rx_work+0x1e1/0x5b0
[    1.518584]  [<ffffffff8107e4bd>] ? process_one_work+0x1ed/0x6b0
[    1.518584]  [<ffffffff8107e538>] process_one_work+0x268/0x6b0
[    1.518584]  [<ffffffff8107e4bd>] ? process_one_work+0x1ed/0x6b0
[    1.518584]  [<ffffffff8107e9c3>] worker_thread+0x43/0x4e0
[    1.518584]  [<ffffffff8107e980>] ? process_one_work+0x6b0/0x6b0
[    1.518584]  [<ffffffff8107e980>] ? process_one_work+0x6b0/0x6b0
[    1.518584]  [<ffffffff8108505f>] kthread+0xdf/0x100
[    1.518584]  [<ffffffff81a4297f>] ret_from_fork+0x1f/0x40
[    1.518584]  [<ffffffff81084f80>] ? kthread_create_on_node+0x210/0x210

Signed-off-by: Arek Lichwa <arek.lichwa@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>