arm64: dts: rockchip: fix rk3399-puma gmac reset gpio

The puma gmac node currently uses opposite active-values for the
gmac phy reset pin. The gpio-declaration uses active-high while the
separate snps,reset-active-low property marks the pin as active low.

While on the kernel side this works ok, other DT users may get
confused - as seen with uboot right now.

So bring this in line and make both properties match, similar to the
other Rockchip board.

Fixes: 2c66fc34 ("arm64: dts: rockchip: add RK3399-Q7 (Puma) SoM")
Signed-off-by: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
Link: https://lore.kernel.org/r/20200603132836.362519-1-heiko@sntech.de