ARM: dts: gemini-dlink-dir-685: rename gpio-i2c to i2c

gemini-dlink-dir-685.dt.yaml: gpio-i2c: $nodename:0: 'gpio-i2c' does not match '^i2c(@.*)?'
>From schema: /usr/src/linux-next/Documentation/devicetree/bindings/i2c/i2c-gpio.yaml

Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>