drm/amdgpu: conduct a proper cleanup of PDB bo

Use amdgpu_bo_free_kernel instead of amdgpu_bo_unref to
perform a proper cleanup of PDB bo.

v2: update subject to be more accurate
Signed-off-by: Guchun Chen <guchun.chen@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c

@@ -1721,7 +1721,7 @@ static int gmc_v9_0_sw_fini(void *handle)
 	amdgpu_gem_force_release(adev);
 	amdgpu_vm_manager_fini(adev);
 	amdgpu_gart_table_vram_free(adev);
-	amdgpu_bo_unref(&adev->gmc.pdb0_bo);
+	amdgpu_bo_free_kernel(&adev->gmc.pdb0_bo, NULL, &adev->gmc.ptr_pdb0);
 	amdgpu_bo_fini(adev);
 
 	return 0;