ARM: dts: hisilicon: fix errors detected by snps-dw-apb-uart.yaml

1. Change node name to match '^serial(@[0-9a-f,]+)*$'
2. Change clock-names to "baudclk", "apb_pclk". Both of them use the same
   clock.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>