ALSA: ymfpci - Don't create invalid PCM & mixers when AC97 doesn't support

- check SDAC bit of AC97 primary codec when create "rear" device 3,
  "4ch" device 2 and "4ch Duplication" switch as the card need a four channels
  AC97 codec to support surround40.

Signed-off-by: Raymond Yau <superquad.vortex2@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/pci/ymfpci/ymfpci.c b/sound/pci/ymfpci/ymfpci.c
index e57b89e8..94ab728 100644
--- a/sound/pci/ymfpci/ymfpci.c
+++ b/sound/pci/ymfpci/ymfpci.c
@@ -286,17 +286,22 @@
 		snd_card_free(card);
 		return err;
 	}
-	if ((err = snd_ymfpci_pcm_4ch(chip, 2, NULL)) < 0) {
+	err = snd_ymfpci_mixer(chip, rear_switch[dev]);
+	if (err < 0) {
 		snd_card_free(card);
 		return err;
 	}
-	if ((err = snd_ymfpci_pcm2(chip, 3, NULL)) < 0) {
-		snd_card_free(card);
-		return err;
-	}
-	if ((err = snd_ymfpci_mixer(chip, rear_switch[dev])) < 0) {
-		snd_card_free(card);
-		return err;
+	if (chip->ac97->ext_id & AC97_EI_SDAC) {
+		err = snd_ymfpci_pcm_4ch(chip, 2, NULL);
+		if (err < 0) {
+			snd_card_free(card);
+			return err;
+		}
+		err = snd_ymfpci_pcm2(chip, 3, NULL);
+		if (err < 0) {
+			snd_card_free(card);
+			return err;
+		}
 	}
 	if ((err = snd_ymfpci_timer(chip, 0)) < 0) {
 		snd_card_free(card);