Bluetooth: Really fix registering hci with duplicate name

Commit fc50744 ("Bluetooth: Fix registering hci with duplicate name") didn't
fully fix the duplicate naming issue with devices, and duplicate device names
could still be created:

[  142.484097] device: 'hci1': device_add
[...]
[  150.545263] device: 'hci1': device_add
[  150.550128] kobject: 'hci1' (ffff880014cc4e58): kobject_add_internal: parent: 'bluetooth', set: 'devices'
[  150.558979] ------------[ cut here ]------------
[  150.561438] WARNING: at fs/sysfs/dir.c:529 sysfs_add_one+0xb0/0xd0()
[  150.572974] Hardware name: Bochs
[  150.580502] sysfs: cannot create duplicate filename '/devices/virtual/bluetooth/hci1'
[  150.584444] Pid: 7563, comm: trinity-child1 Tainted: G        W    3.4.0-next-20120524-sasha #296
[...]

Instead of the weird logic and the attempt at keeping the device list sorted,
just use an IDA.

Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>