drm/amdgpu: always recreate bo_list

The bo_list handle is allocated by OP_CREATE, so in OP_UPDATE here we just
re-create the bo_list object and replace the handle. This way we don't
need locking to protect the bo_list because it's always re-created when
changed.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Chunming Zhou <david1.zhou@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>