ASoC: nau8825: Declare 2 channels for DAI of capture stream

The patch is to make driver with flexibility for more platforms support even if
the internal design is just one ADC. Besides, many I2S controllers only support
2 channels.

Signed-off-by: David Lin <CTLIN0@nuvoton.com>
Link: https://lore.kernel.org/r/20220708054647.540621-1-CTLIN0@nuvoton.com


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