ASoC: Intel: sst: Fix the return value of 'sst_send_byte_stream_mrfld()'

In some error handling paths, an error code is assiegned to 'ret'.
However, the function always return 0.

Fix it and return the error code if such an error paths is taken.

Fixes: 3d9ff346 ("ASoC: Intel: sst: add stream operations")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Mark Brown <broonie@kernel.org>