NET: nl80211, fix lock imbalance and netdev referencing

Stanse found that nl80211_set_wiphy imporperly handles a lock and netdev
reference and contains unreachable code. It is because there return statement
isntead of assignment to result variable. Fix that.

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: "John W. Linville" <linville@tuxdriver.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jouni Malinen <j@w1.fi>
Cc: Samuel Ortiz <sameo@linux.intel.com>
Cc: linux-wireless@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: John W. Linville <linville@tuxdriver.com>