The dai codec needs to ensure that on one dai is used at any time.
This is currently protected by bit atomic operation. With this change,
it done with a mutex instead.

This change is not about functionality or efficiency. It is done with
the hope that it help maintainability in the future.
Suggested-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://lore.kernel.org/r/20191206103542.485224-1-jbrunet@baylibre.comSigned-off-by: Mark Brown <broonie@kernel.org>