ath6kl: fix tx/rx antenna reporting for 2x2 devices

My previous patch incorrectly reported the antenna
for 2x2 devices. It should be a mask instead of
a numeric count. This patch fixes that.

Signed-off-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>