ALSA: hda - Always sync writes in single_cmd mode

In the single_cmd mode, the hardware cannot store the multiple replies
like on RIRB, thus each verb has to sync and wait for the response no
matter whether the return value is needed or not.  Otherwise it may
result in a wrong return value from the previous verb.

Signed-off-by: Takashi Iwai <tiwai@suse.de>