mfd: hisilicon: Use the correct HiSilicon copyright

s/Hisilicon/HiSilicon/

It should use capital S, according to the official website
https://www.hisilicon.com/en

.

Signed-off-by: Hao Fang <fanghao11@huawei.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>