ARM: dts: exynos: Use 'hpd-gpios' instead of 'hpd-gpio'

This patch enables getting a HPD GPIO descriptor quicker.
The exynos-hdmi driver uses "hpd" for HDMI hot plug detection.

	static int hdmi_resources_init(struct hdmi_context *hdata)
	{
		...
		hdata->hpd_gpio = devm_gpiod_get(dev, "hpd", GPIOD_IN);
		...
	}

This calls 'of_find_gpio()' and it generates the GPIO consumer ID by referring
GPIO suffix. So 'hpd-gpios' is preferred on getting a GPIO descriptor.

However, if the device tree uses 'hpd-gpio', then the exynos-hdmi driver
always retries to get a GPIO descriptor because the first GPIO suffix is not
'gpio' but 'gpios'. So you always see the debug message below.

	of_get_named_gpiod_flags: can't parse 'hpd-gpios' property of node '/soc/hdmi@14530000[0]'

Use the preferred property, 'hpd-gpios' instead of 'hpd-gpio'.

Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Cc: devicetree@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-samsung-soc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Milo Kim <woogyom.kim@gmail.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>