sched/core: Refactor the task_flags check for worker sleeping in sched_submit_work()

Simplify the conditional logic for checking worker flags
by splitting the original compound `if` statement into
separate `if` and `else if` clauses.

This modification not only retains the previous functionality,
but also reduces a single `if` check, improving code clarity
and potentially enhancing performance.

Signed-off-by: Wang Jinchao <wangjinchao@xfusion.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/ZOIMvURE99ZRAYEj@fedora