sched/hrtick: Fix hrtick() vs. scheduling context

sched/hrtick: Fix hrtick() vs. scheduling context

The sched_class::task_tick() method is called on the donor
sched_class, and sched_tick() hands it rq->donor as argument,
which is consistent.

However, while hrtick() uses the donor sched_class, it then passes
rq->curr, which is inconsistent. Fix it.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: John Stultz <jstultz@google.com>
Link: https://patch.msgid.link/20250918080205.442967033@infradead.org