ARM: dts: s3c6410: align node SROM bus node name with dtschema in SMDK6410

The SROM controller is modeled with a bus so align the device node name
with dtschema to fix warning:

  srom-cs1@18000000: $nodename:0: 'srom-cs1@18000000'
    does not match '^([a-z][a-z0-9\\-]+-bus|bus|soc|axi|ahb|apb)(@[0-9a-f]+)?$'

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200907183313.29234-6-krzk@kernel.org