bad_page_threshold controls page retirement behavior and it should be
also checked.

v2: simplify the condition of bad page handling path.

Signed-off-by: Tao Zhou <tao.zhou1@amd.com>
Reviewed-by: Stanley.Yang <Stanley.Yang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>