ALSA: pcm: Use a common helper for PCM state check and hwsync
The mostly same codes for checking the current PCM state and calling
hwsync are found in a few places. This patch simplifies them by
creating a common helper function.
It also fixes a couple of cases where we missed the proper state check
(e.g. PAUSED state wasn't handled in rewind and snd_pcm_hwsync()),
too.