cfg80211: add warning when calculating MCS rates >= 32

cfg80211_calculate_bitrate() doesn't work for MCS
rates 32 or higher, and it has always returned 0
in that case. Warn if it ever really happens.
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

net/wireless/util.c

@@ -880,7 +880,7 @@ u16 cfg80211_calculate_bitrate(struct rate_info *rate)
 		return rate->legacy;
 
 	/* the formula below does only work for MCS values smaller than 32 */
-	if (rate->mcs >= 32)
+	if (WARN_ON_ONCE(rate->mcs >= 32))
 		return 0;
 
 	modulation = rate->mcs & 7;