We need to cancel the hci_power_on work in order to avoid it run when we
try to free the hdev.

[ 1434.201149] ------------[ cut here ]------------
[ 1434.204998] WARNING: at lib/debugobjects.c:261 debug_print_object+0x8e/0xb0()
[ 1434.208324] ODEBUG: free active (active state 0) object type: work_struct hint: hci
_power_on+0x0/0x90
[ 1434.210386] Pid: 8564, comm: trinity-child25 Tainted: G        W    3.7.0-rc5-next-
20121112-sasha-00018-g2f4ce0e #127
[ 1434.210760] Call Trace:
[ 1434.210760]  [<ffffffff819f3d6e>] ? debug_print_object+0x8e/0xb0
[ 1434.210760]  [<ffffffff8110b887>] warn_slowpath_common+0x87/0xb0
[ 1434.210760]  [<ffffffff8110b911>] warn_slowpath_fmt+0x41/0x50
[ 1434.210760]  [<ffffffff819f3d6e>] debug_print_object+0x8e/0xb0
[ 1434.210760]  [<ffffffff8376b750>] ? hci_dev_open+0x310/0x310
[ 1434.210760]  [<ffffffff83bf94e5>] ? _raw_spin_unlock_irqrestore+0x55/0xa0
[ 1434.210760]  [<ffffffff819f3ee5>] __debug_check_no_obj_freed+0xa5/0x230
[ 1434.210760]  [<ffffffff83785db0>] ? bt_host_release+0x10/0x20
[ 1434.210760]  [<ffffffff819f4d15>] debug_check_no_obj_freed+0x15/0x20
[ 1434.210760]  [<ffffffff8125eee7>] kfree+0x227/0x330
[ 1434.210760]  [<ffffffff83785db0>] bt_host_release+0x10/0x20
[ 1434.210760]  [<ffffffff81e539e5>] device_release+0x65/0xc0
[ 1434.210760]  [<ffffffff819d3975>] kobject_cleanup+0x145/0x190
[ 1434.210760]  [<ffffffff819d39cd>] kobject_release+0xd/0x10
[ 1434.210760]  [<ffffffff819d33cc>] kobject_put+0x4c/0x60
[ 1434.210760]  [<ffffffff81e548b2>] put_device+0x12/0x20
[ 1434.210760]  [<ffffffff8376a334>] hci_free_dev+0x24/0x30
[ 1434.210760]  [<ffffffff82fd8fe1>] vhci_release+0x31/0x60
[ 1434.210760]  [<ffffffff8127be12>] __fput+0x122/0x250
[ 1434.210760]  [<ffffffff811cab0d>] ? rcu_user_exit+0x9d/0xd0
[ 1434.210760]  [<ffffffff8127bf49>] ____fput+0x9/0x10
[ 1434.210760]  [<ffffffff81133402>] task_work_run+0xb2/0xf0
[ 1434.210760]  [<ffffffff8106cfa7>] do_notify_resume+0x77/0xa0
[ 1434.210760]  [<ffffffff83bfb0ea>] int_signal+0x12/0x17
[ 1434.210760] ---[ end trace a6d57fefbc8a8cc7 ]---

Cc: stable@vger.kernel.org
Reported-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>