ASoC: cs35l56: Remove SDW2RX1 mixer source

The mixer source index value for SDW2RX1 is different between
A1 and B0 silicon. As the driver doesn't provide a DAI for SDW2
just remove it as a mixer source option.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20230418144309.1100721-4-rf@opensource.cirrus.com


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