mac80211: add more missing checks for VHT tx rates

Fixes a crash on attempting to calculate the frame duration for a VHT
packet (which needs to be handled by hw/driver instead).

Reported-by: Jouni Malinen <j@w1.fi>
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 66ddbbe..058686a 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -60,7 +60,7 @@
 	rcu_read_unlock();
 
 	/* assume HW handles this */
-	if (tx->rate.flags & IEEE80211_TX_RC_MCS)
+	if (tx->rate.flags & (IEEE80211_TX_RC_MCS | IEEE80211_TX_RC_VHT_MCS))
 		return 0;
 
 	/* uh huh? */