ath: add a helper for processing reg data on init

This has no functional change. The helper can be used later
for other things like country IE changes and following the CTL
for different countries.

Signed-off-by: Luis R. Rodriguez <mcgrof@qca.qualcomm.com>
Acked-by: Luis R. Rodriguez <mcgrof@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>