[PATCH] ymfpci oops fix

If the driver fails partway through probing, the recovery code will call
ac97_release_codec(NULL), which oopses.

sound/oss/ymfpci.c

@@ -2628,7 +2628,8 @@ static int __devinit ymf_probe_one(struct pci_dev *pcidev, const struct pci_devi
  out_release_region:
 	release_mem_region(pci_resource_start(pcidev, 0), 0x8000);
  out_free:
-	ac97_release_codec(codec->ac97_codec[0]);
+	if (codec->ac97_codec[0])
+		ac97_release_codec(codec->ac97_codec[0]);
 	return -ENODEV;
 }