ASoC: wm8974: fix Boost Mixer Aux Switch

Clear BIT6 of INPPGA means not muted (Switch On).

Signed-off-by: Puyou Lu <puyou.lu@gmail.com>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/1593657025-4903-1-git-send-email-puyou.lu@gmail.com


Signed-off-by: Mark Brown <broonie@kernel.org>