ARM: dts: imx7d-sdb: Fix the SPI chipselect polarity

The following warning is seen when the SPI GPIO driver probes:

gpio-expander@0 enforce active low on chipselect handle

The reason for this warning is clearly explained in the comments inside
drivers/gpio/gpiolib-of.c:

* SPI children have active low chip selects
* by default. This can be specified negatively
* by just omitting "spi-cs-high" in the
* device node, or actively by tagging on
* GPIO_ACTIVE_LOW as flag in the device
* tree. If the line is simultaneously
* tagged as active low in the device tree
* and has the "spi-cs-high" set, we get a
* conflict and the "spi-cs-high" flag will
* take precedence.

To properly represent the SPI chipselect polarity, change it to active-low
when the "spi-cs-high" property is absent.

Signed-off-by: Fabio Estevam <[e-mail]>
Signed-off-by: Shawn Guo <[e-mail]>

arch/arm/boot/dts/imx7d-sdb.dts

···
 		pinctrl-0 = <&pinctrl_spi4>;
 		gpio-sck = <&gpio1 13 GPIO_ACTIVE_HIGH>;
 		gpio-mosi = <&gpio1 9 GPIO_ACTIVE_HIGH>;
-		cs-gpios = <&gpio1 12 GPIO_ACTIVE_HIGH>;
+		cs-gpios = <&gpio1 12 GPIO_ACTIVE_LOW>;
 		num-chipselects = <1>;
 		#address-cells = <1>;
 		#size-cells = <0>;