ASoC: nau8810: change input PGA mixer stage

Organize the paths of the mixer, "Input Boost Stage", including
the routes of the mixer. The control is not used correctly before.
Besides, the driver changes the name of the mixer controls.

Signed-off-by: John Hsu <KCHSU0@nuvoton.com>
Signed-off-by: Mark Brown <broonie@kernel.org>