ath9k: fix channel flag / regd issues with multiple cards

Since the regulatory code touches the channel array, it needs to be
copied for each device instance. That way the original channel array
can also be made const.

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