ARM: dts: gemini: rename mdio to the right name

[ Upstream commit fc5b59b945b546e27977e99a5ca6fe61179ff0d2 ]

ethernet-phy is not the right name for mdio, fix it.

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