cfg80211: add bitrate for 20MHz MCS 9

Some drivers (ath10k) report MCS 9 @ 20MHz, which
technically isn't defined. To get more meaningful value
than 0 out of this however, just extrapolate a bitrate
from ratio of MCS 7 and 9 in channels where it is allowed.

Change-Id: Ia54fce85b570715e705f67bd463c4a219ff71af2
CRs-fixed: 1116687
Signed-off-by: Thomas Pedersen <twp@qca.qualcomm.com>
Cc: Johannes Berg <johannes.berg@intel.com>
Cc: greearb@candelatech.com
Cc: Thomas Pedersen <twp@qca.qualcomm.com>
Patch-mainline: linux-wireless @ 09/10/16, 23:35
Signed-off-by: Peng Xu <pxu@codeaurora.org>

net/wireless/util.c

@@ -1080,7 +1080,7 @@ static u32 cfg80211_calculate_bitrate_vht(struct rate_info *rate)
 		   58500000,
 		   65000000,
 		   78000000,
-		   0,
+		   86500000,
 		},
 		{  13500000,
 		   27000000,