dt-bindings: bus: uniphier-system-bus: fix warning in example

dt-bindings: bus: uniphier-system-bus: fix warning in example

Since commit e69f5dc623f9 ("dt-bindings: serial: Convert 8250 to
json-schema"), the schema for "ns16550a" is checked.

'make dt_binding_check' emits the following warning:

  uart@5,00200000: $nodename:0: 'uart@5,00200000' does not match '^serial(@[0-9a-f,]+)*$'

Rename the node to follow the pattern defined in
Documentation/devicetree/bindings/serial/serial.yaml

While I was here, I removed leading zeros from unit names.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Link: https://lore.kernel.org/r/20200623113242.779241-1-yamada.masahiro@socionext.com
Signed-off-by: Rob Herring <robh@kernel.org>