ath9k_hw: prevent writes to const data on AR9160

Duplicate the data for iniAddac early on, to avoid having to do redundant
memcpy calls later. While we're at it, make AR5416 < v2.2 use the same
codepath. Fixes a reported crash on x86.

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