ASoC: meson: aiu: remove unused encoder structure

Remove an unused structure definition which slipped through the initial
driver submission.

Fixes: 6ae9ca9c ("ASoC: meson: aiu: add i2s and spdif support")
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://lore.kernel.org/r/20200214131350.337968-2-jbrunet@baylibre.com


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