cfg80211: call reg_notifier() once

We are calling the reg_notifier() callback per band, this is
not necessary, just call it once.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>