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.
Reviewed-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>