ARM: dts: exynos: add input clock to CMU in Exynos4412 Odroid

Commit 68605101 ("ARM: dts: exynos: Add support for audio over HDMI
for Odroid X/X2/U3") added assigned clocks under Clock Management Unit.

However the dtschema expects "clocks" property if "assigned-clocks" are
used.  Add reference to input clock to silence the dtschema warnings:

  arch/arm/boot/dts/exynos4412-odroidu3.dt.yaml: clock-controller@10030000: 'clocks' is a dependency of 'assigned-clocks'

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200906142146.21266-2-krzk@kernel.org