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/ls1021a.dtsi b/arch/arm/dts/ls1021a.dtsi
index 7ba2dd2..8aefc82 100644
--- a/arch/arm/dts/ls1021a.dtsi
+++ b/arch/arm/dts/ls1021a.dtsi
@@ -190,7 +190,7 @@
 			interrupts = <GIC_SPI 96 IRQ_TYPE_LEVEL_HIGH>;
 			clock-names = "dspi";
 			clocks = <&platform_clk 1>;
-			num-cs = <6>;
+			spi-num-chipselects = <6>;
 			big-endian;
 			status = "disabled";
 		};
@@ -203,7 +203,7 @@
 			interrupts = <GIC_SPI 97 IRQ_TYPE_LEVEL_HIGH>;
 			clock-names = "dspi";
 			clocks = <&platform_clk 1>;
-			num-cs = <6>;
+			spi-num-chipselects = <6>;
 			big-endian;
 			status = "disabled";
 		};