ARM: dts: exynos: Replace deprecated hsi2c compatible on Exynos5420

Since commit 218e1496 ("i2c: exynos5: add support for HSI2C on
Exynos5260 SoC") the "samsung,exynos5-hsi2c" is deprecated in favor of
SoC version specific: "samsung,exynos5250-hsi2c".

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