ASoC: madera: Update handling of DAPM routes for mono muxed outputs

Correctly link both channels on the DAC if an output muxed between a
stereo and mono output. Without this one channel of the DAC may be
erroneously powered down whilst in mono mode.

Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20200114161841.451-4-ckeepax@opensource.cirrus.com


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