ath5k: fix regression in tx status processing

The regression was introduced in the following commit:

0967e01e
"ath5k: make use of the new rate control API"

ath5k_tx_frame_completed saves the intended per-rate retry counts before
they are cleared by ieee80211_tx_info_clear_status, however at this
point the information in info->status.rates is incomplete.

This causes significant throughput degradation and excessive packet loss
on links where high bit rates don't work properly.

Move the copy from bf->rates a few lines up to ensure that the saved
retry counts are updated, and that they are really cleared in
info->status.rates after the call to ieee80211_tx_info_clear_status.

Cc: stable@vger.kernel.org # 3.10+
Cc: Thomas Huehn <thomas@net.t-labs.tu-berlin.de>
Cc: Benjamin Vahl <bvahl@net.t-labs.tu-berlin.de>
Reported-by: Ben West <ben@gowasabi.net>
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Acked-by: Thomas Huehn <thomas@net.t-labs.tu-berlin.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>