workqueue: Change the code of calculating work_flags in insert_wq_barrier()

mainline inclusion
from mainline-v5.15-rc1
commit d21cece0
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7LRJF

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d21cece0dbb424ad3ff9e49bde6954632b8efede



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Add a local var @work_flags to calculate work_flags step by step, so that
we don't need to squeeze several flags in only the last line of code.

Parepare for next patch to add a bit to barrier work item's flag.  Not
squshing this to next patch makes it clear that what it will have changed.

No functional change intended.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Zeng Heng <zengheng4@huawei.com>