ARM: dts: exynos: Properly override node to use MDMA0 on Universal C210

The Universal C210 (Exynos4210) uses the secure interface of MDMA0,
instead of regular one - non-secure MDMA1.  DTS was overriding MDMA1
node address which caused DTC W=1 warning:

    arch/arm/boot/dts/exynos4.dtsi:707.25-716.6:
        Warning (simple_bus_reg): /soc/amba/mdma@12850000: simple-bus unit address format error, expected "12840000"

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