clk: g12a-aoclk: re-export CLKID_AO_SAR_ADC_SEL clock id

When submitted v2 of the G12A AO-CLK IDs, the SAR_ADC_SEL ID was moved
to the internal non-exported bindings, but this clock is necessary and
mandatory for the SAR ADC bindings.

Export it back to the public bindings.

Fixes: be3d960b ("dt-bindings: clk: add G12A AO Clock and Reset Bindings")
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Acked-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://lkml.kernel.org/r/20190304105358.4987-1-narmstrong@baylibre.com