ARM: socfpga: dts: Add a clock node for sdmmc CIU

The CIU(Card Interface Unit) get its clock from the sdmmc_clk_divided clock
which is used to clock the card. The sdmmc_clk_divided clock is the sdmmc_clk
passed through a fixed divider of 4. This patch adds the sdmmc_clk_divided
node and makes the sdmmc_clk it's parent.
Signed-off-by: Dinh Nguyen <dinguyen@opensource.altera.com>
---
v2: renamed ciu_clk to sdmmc_clk_divided

arch/arm/boot/dts/socfpga.dtsi

@@ -451,6 +451,14 @@ sdmmc_clk: sdmmc_clk {
 						clk-phase = <0 135>;
 					};
 
+					sdmmc_clk_divided: sdmmc_clk_divided {
+						#clock-cells = <0>;
+						compatible = "altr,socfpga-gate-clk";
+						clocks = <&sdmmc_clk>;
+						clk-gate = <0xa0 8>;
+						fixed-divider = <4>;
+					};
+
 					nand_x_clk: nand_x_clk {
 						#clock-cells = <0>;
 						compatible = "altr,socfpga-gate-clk";
@@ -635,7 +643,7 @@ mmc: dwmmc0@ff704000 {
 			fifo-depth = <0x400>;
 			#address-cells = <1>;
 			#size-cells = <0>;
-			clocks = <&l4_mp_clk>, <&sdmmc_clk>;
+			clocks = <&l4_mp_clk>, <&sdmmc_clk_divided>;
 			clock-names = "biu", "ciu";
 		};