Revert "ath9k_hw: reduce ANI firstep range for older chips"

This reverts commit 09efc563

I've received reports that this change is decreasing throughput in some
rare conditions on an AR9280 based device

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