It is perfectly possible that the BO list is created before the BO is
exported. While at it clean up setting shared to one instead of true.

v2: add comment and simplify logic
Signed-off-by: NChristian König <christian.koenig@amd.com>
Reviewed-by: NMichel Dänzer <michel.daenzer@amd.com>
Reviewed-by: NHuang Rui <ray.huang@amd.com>
Acked-by: NJunwei Zhang <Jerry.Zhang@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>