spi: fsl_dspi: rename num-cs to spi-num-chipselects

The official devicetree bindings specifies spi-num-chipselects as the
name. Use it.

Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>
diff --git a/arch/arm/dts/vf.dtsi b/arch/arm/dts/vf.dtsi
index 5ba13dc..1bdaf3d 100644
--- a/arch/arm/dts/vf.dtsi
+++ b/arch/arm/dts/vf.dtsi
@@ -70,7 +70,7 @@
 				#size-cells = <0>;
 				compatible = "fsl,vf610-dspi";
 				reg = <0x4002c000 0x1000>;
-				num-cs = <5>;
+				spi-num-chipselects = <5>;
 				status = "disabled";
 			};
 
@@ -79,7 +79,7 @@
 				#size-cells = <0>;
 				compatible = "fsl,vf610-dspi";
 				reg = <0x4002d000 0x1000>;
-				num-cs = <5>;
+				spi-num-chipselects = <5>;
 				status = "disabled";
 			};