adc: rockchip-saradc: Use vdd-microvolts prop as fallback

Change to use vdd-microvolts prop value as voltage reference when the
supply regulator is missing or when DM_REGULATOR=n is used.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
1 file changed