ARM: dts: imx7d-flex-concentrator: Remove invalid ecspi property

The 'num-chipselects' property is not a valid property for ecspi.

Remove it to fix the following DT check warning:

spi@30630000: Unevaluated properties are not allowed ('num-chipselects' was unexpected)
From schema: Documentation/devicetree/bindings/spi/fsl-imx-cspi.yaml
Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx7d-flex-concentrator.dts

@@ -107,7 +107,6 @@ &adc1 {
 &ecspi2 {
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_ecspi2>;
-	num-chipselects = <1>;
 	cs-gpios = <&gpio4 23 GPIO_ACTIVE_LOW>;
 	status = "okay";
 
@@ -122,7 +121,6 @@ pcf2127: rtc@0 {
 &ecspi4 {
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_ecspi4>;
-	num-chipselects = <1>;
 	cs-gpios = <&gpio3 3 GPIO_ACTIVE_LOW>;
 	status = "okay";