WARN_ON possible buffer overflow and avoid unnecessary dereference.

v2: change BUG_ON to WARN_ON
Signed-off-by: NEvan Quan <evan.quan@amd.com>
Reviewed-by: NHuang Rui <ray.huang@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>