iio: adc: meson-saradc: remove irrelevant clock "sana"

The "sana" clock is not used at SAR ADC module in Amlogic Meson SoC,
it is irrelevant for the SAR ADC.

Signed-off-by: Xingyu Chen <xingyu.chen@amlogic.com>
Signed-off-by: Yixun Lan <yixun.lan@amlogic.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>