ASoC: qcom: Return an error for invalid PCM trigger command

Fix a compile warning
  sound/soc/qcom/lpass-cpu.c: In function ‘lpass_cpu_daiops_trigger’:
  sound/soc/qcom/lpass-cpu.c:224:2: warning: ‘ret’ may be used uninitialized in this function [-Wmaybe-uninitialized]
    return ret;
      ^
Although switch () lists the most of existing cases, it's still better
to cover the rest as an error properly.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Acked-by: Kenneth Westfield <kwestfie@codeaurora.org>
Signed-off-by: Mark Brown <broonie@kernel.org>