[ALSA] Fix AC97 power-saving mode

Fix the bug in AC97 power-saving mode that the power isn't turned on
when power_save is set to 1 via sysfs during the power off state.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>