ASoC: Samsung: Set RFS and BFS in slave mode

As per the User Manual, the RFS and BFS should be set in slave mode
for correct operation.

Signed-off-by: Padmavathi Venna <padma.v@samsung.com>
Signed-off-by: Andrew Bresticker <abrestic@chromium.org>
Reviewed-by: Simon Glass <sjg@google.com>
Signed-off-by: Mark Brown <broonie@linaro.org>