sched/core: Account PSI IRQ time to the execution context

psi_account_irqtime() has two callers which share rq->psi_irq_time, and
they disagree about the context: __schedule() passes the outgoing rq->curr,
sched_tick() passes rq->donor.  Under proxy execution the donor is blocked
on a mutex while rq->curr burns the CPU.

The tick charges PSI_IRQ_FULL to the donor's cgroup and advances the
timestamp, so the call from __schedule() then finds delta <= 0 and charges
nothing.  The delta is not counted twice, it lands on the wrong cgroup.

Pass rq->curr, which is what the call read before commit af0c8b2bf67b
("sched: Split scheduler and execution contexts") renamed curr to donor
across sched_tick().  Without CONFIG_SCHED_PROXY_EXEC the two rq members
are a union, so this only changes anything where that option is set, and
it depends on EXPERT.

Fixes: af0c8b2bf67b ("sched: Split scheduler and execution contexts")
Signed-off-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260918132915.1236312-1-zhanxusheng@xiaomi.com