drivers/perf: hisi_pcie: Initialize event->cpu only on success

Initialize the event->cpu only on success. To be more reasonable
and keep consistent with other PMUs.

Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Link: https://lore.kernel.org/r/20231024092954.42297-3-yangyicong@huawei.com


Signed-off-by: Will Deacon <will@kernel.org>