ath9k: fix rate handling/reporting

This patch fixes some issues introduced in the rate control API rework.
When not running aggregation, copy bf->rates into info->control.rates
before applying the rate control status to it.
In ath_lookup_rate, the rates need to be pulled from bf->rates, not the
tx info.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>