ASoC: Intel: board: Fix missing sentinel for bxt_board_id

ASoC: Intel: board: Fix missing sentinel for bxt_board_id

Without a sentinel in the array of platform devices, we can get a panic
so add a sentinel. Full stack dump below:

[  231.564705] BUG: KASAN: global-out-of-bounds in platform_match+0xb0/0x146
[  231.565500] Read of size 1 at addr ffffffff8380a1a0 by task swapper/0/1
[  231.566280]
[  231.566594] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.12.0-00289-g152771f #1
[  231.567526] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.3-20161025_171302-gandalf 04/01/2014
[  231.568730] Call Trace:
[  231.569128]  dump_stack+0xf8/0x14a
[  231.569615]  print_address_description+0x57/0x1e4
[  231.570216]  ? driver_probe_device+0x814/0x814
[  231.570798]  kasan_report+0x1cb/0x1eb
[  231.571302]  ? platform_match+0xb0/0x146
[  231.571833]  __asan_load1+0x45/0x47
[  231.572324]  platform_match+0xb0/0x146
[  231.572843]  ? platform_uevent+0x73/0x73
[  231.573370]  __driver_attach+0x47/0x16a
[  231.573890]  bus_for_each_dev+0x11a/0x15c
[  231.574422]  ? bus_remove_file+0x57/0x57
[  231.574951]  ? do_raw_spin_unlock+0xc3/0xe0
[  231.575501]  driver_attach+0x2b/0x2e
[  231.576002]  bus_add_driver+0x25e/0x3c5
[  231.576520]  ? set_debug_rodata+0x20/0x20
[  231.584776]  driver_register+0x13e/0x19d
[  231.585305]  __platform_driver_register+0x6c/0x71
[  231.585908]  ? skl_driver_init+0x20/0x20
[  231.586436]  broxton_audio_init+0x17/0x19
[  231.586976]  do_one_initcall+0x11a/0x221
[  231.587499]  ? start_kernel+0x525/0x525
[  231.588020]  ? lock_downgrade+0x281/0x2ec
[  231.588557]  ? trace_hardirqs_on_caller+0x223/0x267
[  231.589169]  ? _raw_spin_unlock_irqrestore+0x49/0x55
[  231.589791]  ? set_debug_rodata+0x20/0x20
[  231.590324]  kernel_init_freeable+0x1fd/0x2b0
[  231.590891]  ? rest_init+0x17c/0x17c
[  231.591384]  kernel_init+0x11/0x157
[  231.591876]  ? rest_init+0x17c/0x17c
[  231.592371]  ret_from_fork+0x2a/0x40
[  231.592865]
[  231.593166] The buggy address belongs to the variable:
[  231.593806]  bxt_board_ids+0x40/0x9e0

Fixes: 152771fbc3 ("ASoC: Intel: board: Add Geminilake platform support")
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Pradeep Tewani <pradeep.d.tewani@intel.com>
Acked-By: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>