dt-bindings: iio: adc: ad7606: Remove spi-cpha from required

The documentation is erroneously stating that spi-cpha is required, and
the example is erroneously setting both spi-cpol and spi-cpha. According
to the datasheet, only cpol should be set.

On zedboard for instance, setting the devicetree as in the example will
simply not work.

Fixes: 416f882c3b ("dt-bindings: iio: adc: Migrate AD7606 documentation to yaml")
Fixes: 6e33a125df ("dt-bindings: iio: adc: Add docs for AD7606 ADC")
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Guillaume Stols <gstols@baylibre.com>
Link: https://patch.msgid.link/20241015-ad7606_add_iio_backend_support-v5-1-654faf1ae08c@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/adc/adi,ad7606.yaml

@@ -39,6 +39,11 @@ properties:
   "#size-cells":
     const: 0
 
+  # According to the datasheet, "Data is clocked in from SDI on the falling
+  # edge of SCLK, while data is clocked out on DOUTA on the rising edge of
+  # SCLK".  Also, even if not stated textually in the datasheet, it is made
+  # clear on the diagrams that sclk idles at high.  Subsequently, in case SPI
+  # interface is used, the correct way is to only set spi-cpol.
   spi-cpha: true
 
   spi-cpol: true
@@ -168,7 +173,6 @@ patternProperties:
 required:
   - compatible
   - reg
-  - spi-cpha
   - avcc-supply
   - vdrive-supply
   - interrupts
@@ -255,7 +259,6 @@ examples:
             reg = <0>;
             spi-max-frequency = <1000000>;
             spi-cpol;
-            spi-cpha;
 
             avcc-supply = <&adc_vref>;
             vdrive-supply = <&vdd_supply>;
@@ -288,7 +291,6 @@ examples:
 
             spi-max-frequency = <1000000>;
             spi-cpol;
-            spi-cpha;
 
             avcc-supply = <&adc_vref>;
             vdrive-supply = <&vdd_supply>;