ASoC: Intel: sst: remove unused ‘ret_val’

In sst_media_close(), 'ret_val' is initialized and assigned as return value
of stream ops close but never used. So remove it.

ound/soc/intel/atom/sst-mfld-platform-pcm.c: In function ‘sst_media_close’:
sound/soc/intel/atom/sst-mfld-platform-pcm.c:360:6: warning: variable ‘ret_val’ set but not used [-Wunused-but-set-variable]
  int ret_val = 0, str_id;

Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>