thinkpad_acpi: Free hotkey_keycode_map after unregistering tpacpi_inputdev

thinkpad_acpi: Free hotkey_keycode_map after unregistering tpacpi_inputdev

We should free hotkey_keycode_map after unregistering tpacpi_inputdev, to aviod
use after free like this:

[   99.408388] =============================================================================
[   99.408393] BUG kmalloc-64 (Not tainted): Poison overwritten
[   99.408394] -----------------------------------------------------------------------------
[   99.408394]
[   99.408398] INFO: 0xf2751962-0xf2751995. First byte 0x98 instead of 0x6b
[   99.408402] INFO: Allocated in 0xfdc88c28 age=79 cpu=0 pid=1329
[   99.408407]  __slab_alloc.isra.50.constprop.56+0x49f/0x533
[   99.408410]  kmem_cache_alloc_trace+0x10d/0x140
[   99.408412]  0xfdc88c28
[   99.408414]  0xfdc898cc
[   99.408417]  do_one_initcall+0x112/0x160
[   99.408420]  sys_init_module+0xe6d/0x1bc0
[   99.408422]  sysenter_do_call+0x12/0x28
[   99.408427] INFO: Freed in hotkey_exit+0x50/0xb0 [thinkpad_acpi] age=14 cpu=1 pid=1333
[   99.408429]  __slab_free+0x3d/0x30b
[   99.408431]  kfree+0x129/0x140
[   99.408435]  hotkey_exit+0x50/0xb0 [thinkpad_acpi]
[   99.408438]  ibm_exit+0xe3/0x1a0 [thinkpad_acpi]
[   99.408441]  thinkpad_acpi_module_exit+0x35/0x208 [thinkpad_acpi]
[   99.408443]  sys_delete_module+0x11f/0x280
[   99.408445]  sysenter_do_call+0x12/0x28
[   99.408447] INFO: Slab 0xf4d5ea20 objects=17 used=17 fp=0x  (null) flags=0x40000080
[   99.408449] INFO: Object 0xf2751960 @offset=2400 fp=0xf2751780
[   99.408449]
[   99.408452] Bytes b4 f2751950: 64 02 00 00 ae ce fe ff 5a 5a 5a 5a 5a 5a 5a 5a  d.......ZZZZZZZZ
[   99.408454] Object f2751960: 6b 6b 98 00 ec 00 8e 00 ee 00 6b 6b e3 00 bf 00 kk........kk....
[   99.408456] Object f2751970: c2 00 6b 6b 6b 6b cd 00 6b 6b 6b 6b 6b 6b e1 00 ..kkkk..kkkkkk..
[   99.408458] Object f2751980: e0 00 e4 00 6b 6b 74 01 73 00 72 00 71 00 94 00 ....kkt.s.r.q...
[   99.408460] Object f2751990: 6b 6b 6b 6b f8 00 6b 6b 6b 6b 6b 6b 6b 6b 6b a5 kkkk..kkkkkkkkk.
[   99.408462] Redzone f27519a0: bb bb bb bb ....

Signed-off-by: Li Dongyang <Jerry87905@gmail.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>