sched: Delete redundant updates to p->prefer_cpus

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7F7KV


CVE: NA

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Delete redundant updates to p->prefer_cpus when smart grid used.
Add missed check for p->prefer_cpus when !CONFIG_QOS_SCHED_SMART_GRID.

Fixes: 21e5d85e ("sched: Fix possible deadlock in tg_set_dynamic_affinity_mode")
Signed-off-by: Hui Tang <tanghui20@huawei.com>
Reviewed-by: Zhang Qiao <zhangqiao22@huawei.com>
Signed-off-by: Zhang Changzhong <zhangchangzhong@huawei.com>
Signed-off-by: Yipeng Zou <zouyipeng@huawei.com>