dt-bindings: iio: adc: update the doc for SAR ADC

Update the doc as the SAR ADC modules doesn't require "sana" clock.

Singed-off-by: Xingyu Chen <xingyu.chen@amlogic.com>
Signed-off-by: Yixun Lan <yixun.lan@amlogic.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/adc/amlogic,meson-saradc.txt

@@ -15,7 +15,6 @@ Required properties:
 			- "clkin" for the reference clock (typically XTAL)
 			- "core" for the SAR ADC core clock
 		optional clocks:
-			- "sana" for the analog clock
 			- "adc_clk" for the ADC (sampling) clock
 			- "adc_sel" for the ADC (sampling) clock mux
 - vref-supply:	the regulator supply for the ADC reference voltage