ath6kl: Remove RSSI update for internal node table

ath6kl does not actually update cfg80211 BSS table when this update
occurs, so there is not much need in updating the internal table
that is not used or exposed.

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