rockchip: dts: firefly using ddr3 1600

According to my test, some of firefly-rk3399 hang after dram init
when using ddr3-1333 config, while using ddr3-1600 config works
for all the board I have test.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>

arch/arm/dts/rk3399-firefly.dts

@@ -8,7 +8,7 @@
 #include <dt-bindings/pwm/pwm.h>
 #include <dt-bindings/pinctrl/rockchip.h>
 #include "rk3399.dtsi"
-#include "rk3399-sdram-ddr3-1333.dtsi"
+#include "rk3399-sdram-ddr3-1600.dtsi"
 
 / {
 	model = "Firefly-RK3399 Board";