ARM: dts: exynos: Enable ADC on Odroid HC1

Odroid HC1 uses the exynos5422-odroid-core.dtsi file as a base.  All
other Exynos5422 Odroids use the "common".  The ADC node was defined
only in the latter.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>