irqchip/hisi: Use the correct HiSilicon copyright

s/Hisilicon/HiSilicon/
It should use capital S, according to
https://www.hisilicon.com/en/terms-of-use

.

Signed-off-by: Hao Fang <fanghao11@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/1617086780-8521-1-git-send-email-fanghao11@huawei.com