ARM: dts: s3c6410: move fixed clocks under root node in SMDK6410

The fixed clocks are kept under dedicated 'clocks' node but this causes
multiple dtschema warnings:

  clocks: $nodename:0: 'clocks' does not match '^([a-z][a-z0-9\\-]+-bus|bus|soc|axi|ahb|apb)(@[0-9a-f]+)?$'
  clocks: #size-cells:0:0: 0 is not one of [1, 2]
  clocks: oscillator@0:reg:0: [0] is too short
  clocks: oscillator@1:reg:0: [1] is too short
  clocks: 'ranges' is a required property
  oscillator@0: 'reg' does not match any of the regexes: 'pinctrl-[0-9]+'

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200907183313.29234-4-krzk@kernel.org