ath6kl: Remove unnecessary bssinfo event header conversion

There is no point in unconditionally converting the bssinfo header
to the old version since only the new header is being used and the
driver can as well read the values from it when needed. Leaving out
the conversion saves some extra memory copying.

In addition, use the calculated "rssi" value snr - 95 dBm to get the
proper value in cfg80211 BSS table (i.e., something that more or less
matches with the value used in STA info).

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>