cfg80211: fix SME association after disassociation

When an AP disassociates us, we currently go into a weird
state because the SME doesn't handle authenticated but not
associated well unless it's within its own state machine,
it can't recover from that. However, it shouldn't need to,
since we don't do any decisions in it really -- so when we
get disconnected, simply deauthenticate too.

Reported-by: Pavel Roskin <proski@gnu.org>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>