ARM: dts: imx6sx: Pass the fsl,fifo-depth property

Like the other mx6 variants, we need to pass fsl,fifo-depth property in dtsi.
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>

arch/arm/boot/dts/imx6sx.dtsi

@@ -306,6 +306,7 @@ ssi1: ssi@02028000 {
 					clock-names = "ipg", "baud";
 					dmas = <&sdma 37 1 0>, <&sdma 38 1 0>;
 					dma-names = "rx", "tx";
+					fsl,fifo-depth = <15>;
 					status = "disabled";
 				};
 
@@ -318,6 +319,7 @@ ssi2: ssi@0202c000 {
 					clock-names = "ipg", "baud";
 					dmas = <&sdma 41 1 0>, <&sdma 42 1 0>;
 					dma-names = "rx", "tx";
+					fsl,fifo-depth = <15>;
 					status = "disabled";
 				};
 
@@ -330,6 +332,7 @@ ssi3: ssi@02030000 {
 					clock-names = "ipg", "baud";
 					dmas = <&sdma 45 1 0>, <&sdma 46 1 0>;
 					dma-names = "rx", "tx";
+					fsl,fifo-depth = <15>;
 					status = "disabled";
 				};