cfg80211: fix static regdomains

When Luis added the static regdomains back he used +/-20
of the centre frequencies to account for 40MHz bandwidth
neglecting the fact that 40MHz bandwidth cannot be used
on the channels close to the allowed band edges.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>