ALSA: hda/realtek - Comprehensive model list for ALC268

Add the missing entry for ALC268 model strings.
Only "spdif" was missing, and that's it.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

Documentation/sound/hd-audio/models.rst

@@ -41,6 +41,8 @@ inv-dmic
     Inverted internal mic workaround
 hp-eapd
     Disable HP EAPD on NID 0x15
+spdif
+    Enable SPDIF output on NID 0x1e
 
 ALC22x/23x/25x/269/27x/28x/29x (and vendor-specific ALC3xxx models)
 ===================================================================

sound/pci/hda/patch_realtek.c

@@ -2688,6 +2688,7 @@ static const struct hda_fixup alc268_fixups[] = {
 static const struct hda_model_fixup alc268_fixup_models[] = {
 	{.id = ALC268_FIXUP_INV_DMIC, .name = "inv-dmic"},
 	{.id = ALC268_FIXUP_HP_EAPD, .name = "hp-eapd"},
+	{.id = ALC268_FIXUP_SPDIF, .name = "spdif"},
 	{}
 };