rockchip: Disable sdio mmc slot on rk3288-firefly

U-Boot can't use the sdio card so turn it of to prevent things getting
confused/struck when trying to use the card as storage.
Signed-off-by: NSjoerd Simons <sjoerd.simons@collabora.co.uk>
Acked-by: NSimon Glass <sjg@chromium.org>
Signed-off-by: NSimon Glass <sjg@chromium.org>

arch/arm/dts/rk3288-firefly.dtsi

@@ -386,7 +386,7 @@
 	pinctrl-names = "default";
 	pinctrl-0 = <&sdio0_bus4>, <&sdio0_cmd>, <&sdio0_clk>;
 	vmmc-supply = <&vcc_18>;
-	status = "okay";
+	status = "disabled";
 };
 
 &sdmmc {