Fix the wrong objects comparing in the Yunikorn-core sorts.go

yunikorn-core/[pkg|https://github.com/apache/yunikorn-core/tree/master/pkg]/[scheduler|https://github.com/apache/yunikorn-core/tree/master/pkg/scheduler]/[objects|https://github.com/apache/yunikorn-core/tree/master/pkg/scheduler/objects]/sorters.go

In 158 line, the submission time compare  seems wrong. **