ALSA: Fix AC97 power down

Some laptops don't like PR3 powerdown.  Do PR3 powerdown only
for the real power-saving.
Signed-off-by: NTakashi Iwai <tiwai@suse.de>
Signed-off-by: NJaroslav Kysela <perex@perex.cz>

sound/pci/ac97/ac97_codec.c

@@ -2295,9 +2295,11 @@ static void snd_ac97_powerdown(struct snd_ac97 *ac97)
 	power |= AC97_PD_PR0 | AC97_PD_PR1;	/* ADC & DAC powerdown */
 	snd_ac97_write(ac97, AC97_POWERDOWN, power);
 	udelay(100);
-	power |= AC97_PD_PR2 | AC97_PD_PR3;	/* Analog Mixer powerdown */
+	power |= AC97_PD_PR2;	/* Analog Mixer powerdown (Vref on) */
 	snd_ac97_write(ac97, AC97_POWERDOWN, power);
 	if (ac97_is_power_save_mode(ac97)) {
+		power |= AC97_PD_PR3;	/* Analog Mixer powerdown */
+		snd_ac97_write(ac97, AC97_POWERDOWN, power);
 		udelay(100);
 		/* AC-link powerdown, internal Clk disable */
 		/* FIXME: this may cause click noises on some boards */