ASoC: Intel: Skylake: remove unused 'ret'

In skl_tplg_mixer_dapm_post_pmd_event(), a variable 'ret' is initialized but
not used.

We don't check return of skl_delete_pipe, so remove the assignment as
well, so remove this variable.

sound/soc/intel/skylake/skl-topology.c: In function ‘skl_tplg_mixer_dapm_post_pmd_event’:
sound/soc/intel/skylake/skl-topology.c:976:6: warning: variable ‘ret’ set but not used [-Wunused-but-set-variable]
  int ret = 0;
      ^
Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>