drm/amdgpu: clean up bo in vce and vcn test

drm/amdgpu: clean up bo in vce and vcn test

BO created with amdgpu_bo_create_reserved() wasn't clean
properly before, which causes:

[   21.056218] WARNING: CPU: 0 PID: 7 at drivers/gpu/drm/ttm/ttm_bo.c:518 ttm_bo_release+0x2bf/0x310 [ttm]
<snip>
[   21.056430] Call Trace:
[   21.056525]  amdgpu_bo_unref+0x1a/0x30 [amdgpu]
[   21.056635]  amdgpu_vcn_dec_send_msg+0x1b2/0x270 [amdgpu]
[   21.056740]  amdgpu_vcn_dec_get_create_msg.constprop.0+0xd8/0x100 [amdgpu]
[   21.056843]  amdgpu_vcn_dec_ring_test_ib+0x27/0x180 [amdgpu]
[   21.056936]  amdgpu_ib_ring_tests+0xf1/0x150 [amdgpu]
[   21.057024]  amdgpu_device_delayed_init_work_handler+0x11/0x30 [amdgpu]
[   21.057030]  process_one_work+0x1df/0x370
[   21.057033]  worker_thread+0x46/0x340
[   21.057034]  ? process_one_work+0x370/0x370
[   21.057037]  kthread+0x11b/0x140
[   21.057039]  ? __kthread_bind_mask+0x60/0x60
[   21.057043]  ret_from_fork+0x22/0x30

Signed-off-by: Nirmoy Das <nirmoy.das@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/406382/
Signed-off-by: Christian König <christian.koenig@amd.com>