ASoC: msm: flush if prior and current backends rate not matching

It is found that during device switch from one backend
with one sample rate to another backend with another sample rate
the command to QDSP6 ADM which maps audio stream session to a
particular backend would not get carried out until pending
data of audio stream session from previous backend is either
read out or flushed. This scenario occurs when application
stops providing more buffers to retrieve captured data.
Remedy is to flush upon detection of rate mismatching.

Change-Id: I8284dd076af4c625268a9c6a5f45c3f6146e5c14
Signed-off-by: Damir Didjusto <damird@codeaurora.org>
Signed-off-by: Vimal Puthanveed <vimalp@codeaurora.org>