ath9k: Fix address management

Since both the arguments need to satisfy
the alignment requirements of ether_addr_copy(),
use memcpy() in cases where there will be no
big performance benefit and make sure that
ether_addr_copy() calls use properly aligned
arguments.

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>