ALSA: HDA: Fix internal microphone on Dell Studio 16 XPS 1645

More than one user reports that changing the model from "both" to
"dmic" makes their Internal Mic work.

Cc: stable@kernel.org
Tested-by: Martin Ling <martin-launchpad@earth.li>
BugLink: https://bugs.launchpad.net/bugs/795823
Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/hda/patch_sigmatel.c

@@ -1596,7 +1596,7 @@ static const struct snd_pci_quirk stac92hd73xx_cfg_tbl[] = {
 	SND_PCI_QUIRK(PCI_VENDOR_ID_DELL, 0x02bd,
 				"Dell Studio 1557", STAC_DELL_M6_DMIC),
 	SND_PCI_QUIRK(PCI_VENDOR_ID_DELL, 0x02fe,
-				"Dell Studio XPS 1645", STAC_DELL_M6_BOTH),
+				"Dell Studio XPS 1645", STAC_DELL_M6_DMIC),
 	SND_PCI_QUIRK(PCI_VENDOR_ID_DELL, 0x0413,
 				"Dell Studio 1558", STAC_DELL_M6_DMIC),
 	{} /* terminator */