ath79: drop num-cs for SPI controller

None of the spi drivers on ath79 uses the num-cs property.

Cc: Chuanhong Guo <gch981213@gmail.com>
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Acked-by: Chuanhong Guo <gch981213@gmail.com>

target/linux/ath79/dts/qca9531_comfast_cf-e560ac.dts

@@ -83,8 +83,6 @@
 &spi {
 	status = "okay";
 
-	num-cs = <1>;
-
 	flash@0 {
 		compatible = "jedec,spi-nor";
 		reg = <0>;