[ALSA] ac97 - Fix potential negative array index

Fix the case cidx2 >= 0 and cidx2 < 0 which may result in negative
array index.
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>

sound/pci/ac97/ac97_patch.c

@@ -1467,7 +1467,9 @@ static void patch_ad1881_chained(struct snd_ac97 * ac97, int unchained_idx, int
 	snd_ac97_write_cache(ac97, AC97_AD_CODEC_CFG, 0x0002);		// ID1C
 	ac97->spec.ad18xx.codec_cfg[unchained_idx] = 0x0002;
 	if (cidx1 >= 0) {
-		if (patch_ad1881_chained1(ac97, cidx1, 0x0006))		// SDIE | ID1C
+		if (cidx2 < 0)
+			patch_ad1881_chained1(ac97, cidx1, 0);
+		else if (patch_ad1881_chained1(ac97, cidx1, 0x0006))	// SDIE | ID1C
 			patch_ad1881_chained1(ac97, cidx2, 0);
 		else if (patch_ad1881_chained1(ac97, cidx2, 0x0006))	// SDIE | ID1C
 			patch_ad1881_chained1(ac97, cidx1, 0);