cfg80211: properly name driver locking

Currently we call that cfg80211_put_dev(), but that is
misleading. With the new convention of using 'rdev' for
registered_device variables, also call that function
cfg80211_unlock_rdev().

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