ttm_bo_glob and ttm_mem_glob are defined as structure instance, while
not allocated by kzalloc, so kfree should not be invoked to release
them anymore. Otherwise, it will cause the following kernel BUG when
unloading amdgpu module

[   48.419294] kernel BUG at /build/linux-5s7Xkn/linux-4.15.0/mm/slub.c:3894!
[   48.419352] invalid opcode: 0000 [#1] SMP PTI
[   48.419387] Modules linked in: amdgpu(OE-) amdchash(OE) amdttm(OE) amd_sched(OE) amdkcl(OE) amd_iommu_v2 drm_kms_helper drm i2c_algo_bit fb_sys_fops syscopyarea sysfillrect sysimgblt snd_hda_codec_generic snd_hda_intel snd_hda_codec snd_hda_core snd_hwdep kvm_intel kvm irqbypass crct10dif_pclmul crc32_pclmul ghash_clmulni_intel snd_pcm snd_seq_midi snd_seq_midi_event snd_rawmidi pcbc snd_seq snd_seq_device snd_timer aesni_intel snd soundcore joydev aes_x86_64 crypto_simd glue_helper cryptd input_leds mac_hid serio_raw binfmt_misc nfsd auth_rpcgss nfs_acl lockd grace sunrpc sch_fq_codel parport_pc ppdev lp parport ip_tables x_tables autofs4 8139too psmouse i2c_piix4 8139cp mii floppy pata_acpi
[   48.419782] CPU: 1 PID: 1281 Comm: modprobe Tainted: G           OE    4.15.0-20-generic #21-Ubuntu
[   48.419838] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
[   48.419901] RIP: 0010:kfree+0x137/0x180
[   48.419934] RSP: 0018:ffffb02101273bf8 EFLAGS: 00010246
[   48.419974] RAX: ffffeee1418ad7e0 RBX: ffffffffc075f100 RCX: ffff8fed7fca7ed0
[   48.420025] RDX: 0000000000000000 RSI: 000000000003440e RDI: 0000000022400000
[   48.420073] RBP: ffffb02101273c10 R08: 0000000000000010 R09: ffff8fed7ffd3680
[   48.420121] R10: ffffeee1418ad7c0 R11: ffff8fed7ffd3000 R12: ffffffffc075e2c0
[   48.420169] R13: ffffffffc074ec10 R14: ffff8fed73063900 R15: ffff8fed737428e8
[   48.420216] FS:  00007fdc912ec540(0000) GS:ffff8fed7fc80000(0000) knlGS:0000000000000000
[   48.420267] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   48.420308] CR2: 000055fa40c30060 CR3: 000000023470a006 CR4: 00000000003606e0
[   48.420358] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   48.420405] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   48.420452] Call Trace:
[   48.420485]  ttm_bo_global_kobj_release+0x20/0x30 [amdttm]
[   48.420528]  kobject_release+0x6a/0x180
[   48.420562]  kobject_put+0x28/0x50
[   48.420595]  ttm_bo_global_release+0x36/0x50 [amdttm]
[   48.420636]  amdttm_bo_device_release+0x119/0x180 [amdttm]
[   48.420678]  ? amdttm_bo_clean_mm+0xa6/0xf0 [amdttm]
[   48.420760]  amdgpu_ttm_fini+0xc9/0x180 [amdgpu]
[   48.420821]  amdgpu_bo_fini+0x12/0x40 [amdgpu]
[   48.420889]  gmc_v9_0_sw_fini+0x40/0x50 [amdgpu]
[   48.420947]  amdgpu_device_fini+0x36f/0x4c0 [amdgpu]
[   48.421007]  amdgpu_driver_unload_kms+0xb4/0x150 [amdgpu]
[   48.421058]  drm_dev_unregister+0x46/0xf0 [drm]
[   48.421102]  drm_dev_unplug+0x12/0x70 [drm]
Signed-off-by: Trigger Huang <Trigger.Huang@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>