ath11k: fix incorrect peer stats counters update

Convert mac80211 bw to ath11k bw before updating peer stats
bw counters, which fixes incorrect peer stats counters update.

Signed-off-by: Venkateswara Naralasetty <vnaralas@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>