ASoC: rt1015: Remove unnecessary flush work on rt1015 driver

Remove workqueue of flush work in rt1015 driver since we don't need it
after internal discussion, and there is no impact on performance
without this workqueue.

Signed-off-by: Jack Yu <jack.yu@realtek.com>
Link: https://lore.kernel.org/r/3ef458a6ad754589b96d6a94abda1e55@realtek.com


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