ARM: dts: samsung: exynos5250-snow: switch i2c-arb to new child variant

Since commit e8813c15

 ("dt-bindings: i2c: add support for 'i2c-arb'
subnode") the i2c-arbitrator subnode should not have unit address.

Link: https://lore.kernel.org/r/20230721133246.15752-2-krzysztof.kozlowski@linaro.org
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>