ath10k: fix recent bandwidth conversion bug

ath10k: fix recent bandwidth conversion bug

The commit "cfg80211: make RATE_INFO_BW_20 the default" changed
the index of RATE_INFO_BW_20, but the updates to ath10k missed
the special bandwidth calculation case in
ath10k_update_per_peer_tx_stats().

This will fix below warning,

 WARNING: CPU: 0 PID: 609 at net/wireless/util.c:1254
 cfg80211_calculate_bitrate+0x174/0x220
 invalid rate bw=1, mcs=9, nss=2

 (unwind_backtrace) from
 (cfg80211_calculate_bitrate+0x174/0x220)
 (cfg80211_calculate_bitrate) from
 (nl80211_put_sta_rate+0x44/0x1dc)from
 (nl80211_put_sta_rate) from
 (nl80211_send_station+0x388/0xaf0)
 (nl80211_get_station+0xa8/0xec)
 [ end trace da8257d6a850e91a ]

Fixes: 842be75c77cb ("cfg80211: make RATE_INFO_BW_20 the default")
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
Signed-off-by: Anilkumar Kolli <akolli@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>