Add guard for NULL pointer access
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Charlene Liu <charlene.liu@amd.com>
Acked-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Johnson Chen <johnson.chen@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>