sched/fair: fix the comment for PREEMPT_SHORT

We do not have RESPECT_SLICE, we only have RUN_TO_PARITY.
Change RESPECT_SLICE to RUN_TO_PARITY, makes it more clear.

Signed-off-by: Huang Shijie <shijie@os.amperecomputing.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Christoph Lameter (Ampere) <cl@linux.com>
Link: https://lkml.kernel.org/r/20241001070456.10939-1-shijie@os.amperecomputing.com