ASoC: SOF: ipc: use snd_sof_pcm_period_elapsed

Switch to a wrapper function which schedules the actual call of
snd_pcm_period_elapsed after the current IPC is completed.

Signed-off-by: Keyon Jie <yang.jie@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>