adc: common: handle gain of 128 in adc_gain_invert()

Add missing entry for ADC_GAIN_128 in the adc_gain_invert() function.

This fixes 4420c5ed40f4363b58e1fb800a8b6be483f7b1fe.

Signed-off-by: Henrik Brix Andersen <hebad@vestas.com>
1 file changed