rockchip: dts: rk3399-firely: add 'same-as-spl'

Like on rk3399-puma we want to continue booting the fill U-Boot from
the same device as the SPL stage.

Signed-off-by: Mark Kettenis <kettenis@openbsd.org>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
diff --git a/arch/arm/dts/rk3399-firefly.dts b/arch/arm/dts/rk3399-firefly.dts
index be35086..f90e7e8 100644
--- a/arch/arm/dts/rk3399-firefly.dts
+++ b/arch/arm/dts/rk3399-firefly.dts
@@ -15,7 +15,7 @@
 
 	chosen {
 		stdout-path = &uart2;
-		u-boot,spl-boot-order = &sdhci, &sdmmc;
+		u-boot,spl-boot-order = "same-as-spl", &sdhci, &sdmmc;
 	};
 
 	backlight: backlight {