ASoC: fsl_sai: Don't reset FIFO until TE/RE bit is unset

TE/RE bit of T/RCSR will remain set untill the current frame is physically
finished. The FIFO reset operation should wait this bit's totally cleared
rather than ignoring its status which might cause TE/RE disabling failed.

This patch adds delay and timeout to wait for its completion before FIFO
reset.

Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
Signed-off-by: Mark Brown <broonie@linaro.org>