overlays: sc16is75x: Fix spi1 cs-gpios

Native cs is somewhat broken on spi1 (see [1]), so re-add the explicit
cs-gpios definition, as was done before in sc16is752-spi1-overlay.

Fixes #6962

[1] torvalds/linux@519f2c2

Signed-off-by: Nicolai Buchwitz <[email protected]>

Author: nbuchwitz

arch/arm/boot/dts/overlays/sc16is75x-spi-overlay.dts

@@ -79,7 +79,8 @@
 			<&sc16is75x_pins>, "name=sc16is75x_spi0_1_pins";
 		spi1-0 = <0>, "-0",
 			<&sc16is75x_frag>, "target:0=", <&spi1>,
-			<&sc16is75x_pins>, "name=sc16is75x_spi1_0_pins";
+			<&sc16is75x_pins>, "name=sc16is75x_spi1_0_pins",
+			<&sc16is75x>, "cs-gpios:0=", <&gpio 18 1>;
 		spi1-1 = <0>, "-0",
 			<&sc16is75x_frag>, "target:0=", <&spi1>,
 			<&sc16is75x>, "reg:0=1",