ASoC: cs4270: fix Master Capture Switch polarity

The control modifies the MUTE register, hence the polarity must be
inverted.

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Acked-By: Timur Tabi <timur@freescale.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>