ARM: dts: exynos: Silence DP HPD pinctrl dtschema warning in Exynos5250 Spring

The pin configuration of Display Port HPD GPIO emds with '-gpio' which
confuses dtschema:

  arch/arm/boot/dts/exynos5250-spring.dt.yaml: pinctrl@11400000: dp-hpd-gpio:
    {'samsung,pins': ['gpc3-0'], ... 'samsung,pin-drv': [[0]], 'phandle': [[23]]} is not of type 'array'
    From schema: lib/python3.6/site-packages/dtschema/schemas/gpio/gpio-consumer.yaml

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200901075417.22481-11-krzk@kernel.org