ASoC: sgtl5000: Fix voltage units in dev_err message

vdda, vddio and vddd are voltages expressed in milivolts (mV), so use the
proper annotation.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>