drivers/perf: hisi: Don't update the associated_cpus on CPU offline

drivers/perf: hisi: Don't update the associated_cpus on CPU offline

Event will be scheduled on CPU of hisi_pmu::on_cpu which is selected
from the intersection of hisi_pmu::associated_cpus and online CPUs.
So the associated_cpus don't need to be maintained with online CPUs.
This will save one update operation if one associated CPU is offlined.

Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Link: https://lore.kernel.org/r/20241210141525.37788-3-yangyicong@huawei.com
Signed-off-by: Will Deacon <will@kernel.org>