ARM: dts: gemini-dlink-dns-313: rename gpio-i2c to i2c

This fixes dtcheck warning:
arch/arm/boot/dts/gemini-dlink-dns-313.dt.yaml: gpio-i2c: $nodename:0: 'gpio-i2c' does not match '^i2c(@.*)?'

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