ath9k: Fix hw crypto configuration for TKIP in AP mode

Incorrect Michael MIC key (RX, should have been TX) was set for the
group key in AP mode. This resulted in all broadcast frames triggering
Michael MIC errors and eventual TKIP countermeasures. The change here
sets the correct Michael MIC key based on whether the local end is the
authenticator (well, AP for now).

Signed-off-by: Jouni Malinen <jouni.malinen@atheros.com>
Tested-by: Pat Erley <pat-lkml@erley.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>