ad5593/ad5593.cpp: Fix pin function bug when changing from DAC to ADC

In case a pin was configured with function DAC and is afterwards set
to ADC. The pin would still read the previous set voltage.

Fixed by clearing the DAC ENABLE bit.

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>

ad5593/ad5593.cpp

@@ -147,6 +147,7 @@ void io::function(IoFunction func)
 	switch (func)
 	{
 	case ADC:
+		ClearBit(dac_en);
 		SetBit(adc_en);
 		ClearBit(gpio_out);
 		ClearBit(gpio_in);