ALSA: hda - Add quirk for ASUS G751 laptop

ASUS G751 requires the extra COEF initialization to make it microphone
working properly.
Reported-and-tested-by: Håvard <hovardslill@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/hda/patch_realtek.c

@@ -7738,6 +7738,7 @@ enum {
 	ALC662_FIXUP_ASUS_Nx50,
 	ALC668_FIXUP_ASUS_Nx51_HEADSET_MODE,
 	ALC668_FIXUP_ASUS_Nx51,
+	ALC668_FIXUP_ASUS_G751,
 	ALC891_FIXUP_HEADSET_MODE,
 	ALC891_FIXUP_DELL_MIC_NO_PRESENCE,
 	ALC662_FIXUP_ACER_VERITON,
@@ -8007,6 +8008,14 @@ static const struct hda_fixup alc662_fixups[] = {
 		.chained = true,
 		.chain_id = ALC668_FIXUP_ASUS_Nx51_HEADSET_MODE,
 	},
+	[ALC668_FIXUP_ASUS_G751] = {
+		.type = HDA_FIXUP_VERBS,
+		.v.verbs = (const struct hda_verb[]) {
+			{ 0x20, AC_VERB_SET_COEF_INDEX, 0xc3 },
+			{ 0x20, AC_VERB_SET_PROC_COEF, 0x4000 },
+			{}
+		},
+	},
 	[ALC891_FIXUP_HEADSET_MODE] = {
 		.type = HDA_FIXUP_FUNC,
 		.v.func = alc_fixup_headset_mode,
@@ -8080,6 +8089,7 @@ static const struct snd_pci_quirk alc662_fixup_tbl[] = {
 	SND_PCI_QUIRK(0x1043, 0x11cd, "Asus N550", ALC662_FIXUP_ASUS_Nx50),
 	SND_PCI_QUIRK(0x1043, 0x13df, "Asus N550JX", ALC662_FIXUP_BASS_1A),
 	SND_PCI_QUIRK(0x1043, 0x129d, "Asus N750", ALC662_FIXUP_ASUS_Nx50),
+	SND_PCI_QUIRK(0x1043, 0x12ff, "ASUS G751", ALC668_FIXUP_ASUS_G751),
 	SND_PCI_QUIRK(0x1043, 0x1477, "ASUS N56VZ", ALC662_FIXUP_BASS_MODE4_CHMAP),
 	SND_PCI_QUIRK(0x1043, 0x15a7, "ASUS UX51VZH", ALC662_FIXUP_BASS_16),
 	SND_PCI_QUIRK(0x1043, 0x177d, "ASUS N551", ALC668_FIXUP_ASUS_Nx51),