ath9k_hw: remove function pointer abstraction for internal ANI ops

The code gets more concise and readable when making the new ANI functions
fall back to the old ones if ANI v2 is disabled. This also makes further code
cleanup easier.

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