ALSA: intel8x0 - add Dell Optiplex GX620 (AD1981B) to AC97 clock whitelist

alsa-info.sh output at:
https://bugzilla.redhat.com/show_bug.cgi?id=441087#c49

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

sound/pci/intel8x0.c

@@ -2702,6 +2702,7 @@ static struct snd_pci_quirk intel8x0_clock_list[] __devinitdata = {
 	SND_PCI_QUIRK(0x0e11, 0x008a, "AD1885", 41000),
 	SND_PCI_QUIRK(0x1028, 0x00be, "AD1885", 44100),
 	SND_PCI_QUIRK(0x1028, 0x0177, "AD1980", 48000),
+	SND_PCI_QUIRK(0x1028, 0x01ad, "AD1981B", 48000),
 	SND_PCI_QUIRK(0x1043, 0x80f3, "AD1985", 48000),
 	{ }	/* terminator */
 };