ALSA: hda - Fix digital mic on dell-m4-1 and dell-m4-3

Fix num_dmuxes initialization for dell-m4-1 and dell-m4-3 models
of IDT 92HD71bxx codec, which was wrongly set to zero.

Cc: <stable@kernel.org>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>

sound/pci/hda/patch_sigmatel.c

@@ -4989,7 +4989,7 @@ static int patch_stac92hd71bxx(struct hda_codec *codec)
 	case STAC_DELL_M4_3:
 		spec->num_dmics = 1;
 		spec->num_smuxes = 0;
-		spec->num_dmuxes = 0;
+		spec->num_dmuxes = 1;
 		break;
 	default:
 		spec->num_dmics = STAC92HD71BXX_NUM_DMICS;