ASoC: tegra: tegra20_das: Remove unused function tegra20_das_read

This function is unused since commit 7203a625 ("ASoC: convert
Tegra20 DAS driver to regmap").

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20220629194224.175607-2-u.kleine-koenig@pengutronix.de


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