ASoC: wm8960: boost switch should be closed when using L/RINPUT1

L/RINPUT1 can line to Left/Right Boost Mixer through boost switch.
If boost switch is open, there will be no voice when using L/RINPUT1.

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>