[ALSA] Restore the default value after rate detection

AC97 Codec
Restore the default value of rate registers after detection of available
rates.  This might fix the problem of playback noises on some mobo drivers.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/ac97/ac97_codec.c

@@ -1595,6 +1595,7 @@ static int snd_ac97_test_rate(ac97_t *ac97, int reg, int shadow_reg, int rate)
 static void snd_ac97_determine_rates(ac97_t *ac97, int reg, int shadow_reg, unsigned int *r_result)
 {
 	unsigned int result = 0;
+	unsigned short saved;
 
 	if (ac97->bus->no_vra) {
 		*r_result = SNDRV_PCM_RATE_48000;
@@ -1604,6 +1605,7 @@ static void snd_ac97_determine_rates(ac97_t *ac97, int reg, int shadow_reg, unsi
 		return;
 	}
 
+	saved = snd_ac97_read(ac97, reg);
 	if ((ac97->ext_id & AC97_EI_DRA) && reg == AC97_PCM_FRONT_DAC_RATE)
 		snd_ac97_update_bits(ac97, AC97_EXTENDED_STATUS,
 				     AC97_EA_DRA, 0);
@@ -1642,6 +1644,10 @@ static void snd_ac97_determine_rates(ac97_t *ac97, int reg, int shadow_reg, unsi
 		snd_ac97_update_bits(ac97, AC97_EXTENDED_STATUS,
 				     AC97_EA_DRA, 0);
 	}
+	/* restore the default value */
+	snd_ac97_write_cache(ac97, reg, saved);
+	if (shadow_reg)
+		snd_ac97_write_cache(ac97, shadow_reg, saved);
 	*r_result = result;
 }