ASoC: wm8960: correct the max register value of mic boost pga

the max register value of mic boost pga should be 3.

Signed-off-by: Zidan Wang <zidan.wang@freescale.com>
Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
1 file changed