cfg80211: do not iterate over rdev list on country IE hint

Simplify the country IE hint code by just bailing out if
a previous country IE has been issued. We currently just trust
the first AP we connect to on any card. The idea was to perform
conflict resolution within this routine but since we can no longer
iterate over the registered device list here we leave conflict
resolution to be dealt with at a later time on the workqueue.

This code has no functional changes other than saving us an
interation over the registered device list when a second card
is connected, or you unplug and connect the same one, and a
country IE is received. This would have been done upon every
beacon received.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>