soundwire: qcom: wait for fifo to be empty before suspend

Wait for Fifo to be empty before going to suspend or before bank
switch happens. Just to make sure that all the reads/writes are done.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20230525133812.30841-3-srinivas.kandagatla@linaro.org


Signed-off-by: Vinod Koul <vkoul@kernel.org>