ath6kl: add support for FW API 3

As firmware starting from 3.2.0.12 has some API changes and doesn't work
with older versions of ath6kl we need to bump up the API version. This
way we don't break anything.

Also store which version of API is used and print that during boot:

ath6kl: ar6003 hw 2.1.1 sdio fw 3.2.0.13 api 3

Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>