According to UEFI spec, unsupported function should return EFI_UNSUPPORTED directly. Cc: Eric Dong <eric.dong@intel.com> Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Jiewen Yao <jiewen.yao@intel.com> Reviewed-by: Eric Dong <eric.dong@intel.com>