mac80211: off by one in mcs mask handling

"ridx" is used as an index into the mcs_mask[] array which has
IEEE80211_HT_MCS_MASK_LEN elements.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/wireless/nl80211.c

@@ -5410,7 +5410,7 @@ static bool ht_rateset_to_mask(struct ieee80211_supported_band *sband,
 		rbit = BIT(rates[i] % 8);
 
 		/* check validity */
-		if ((ridx < 0) || (ridx > IEEE80211_HT_MCS_MASK_LEN))
+		if ((ridx < 0) || (ridx >= IEEE80211_HT_MCS_MASK_LEN))
 			return false;
 
 		/* check availability */