ALSA: Reduce stall detection timeout in riptide.c

Reduce the command timeout to 0.5sec. Should be enough to allow a
working command interface but removes a RCU stall and slow resume on
some revisions where the AC97 revision detection stalls in resume.

Signed-off-by: Peter Gruber <nokos@gmx.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>