ARM: dts: imx6sll: add missing properties for sram

All 3 properties are required by sram.yaml. Fixes the dtbs_check warning:
sram@900000: '#address-cells' is a required property
sram@900000: '#size-cells' is a required property
sram@900000: 'ranges' is a required property
Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6sll.dtsi

@@ -115,6 +115,9 @@ soc {
 		ocram: sram@900000 {
 			compatible = "mmio-sram";
 			reg = <0x00900000 0x20000>;
+			ranges = <0 0x00900000 0x20000>;
+			#address-cells = <1>;
+			#size-cells = <1>;
 		};
 
 		intc: interrupt-controller@a01000 {