ALSA: Au1xpsc: psc not disabled when TX is idle

TX idleness isn't tested, but RX twice. PSC is not disabled when TX is idle

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Acked-by: Manuel Lauss <mano@roarinelk.homelinux.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>