[PATCH] softmac: fix unbalanced mutex_lock/unlock in ieee80211softmac_wx_set_mlme

Routine ieee80211softmac_wx_set_mlme has one return that fails
to release a mutex acquired at entry.

Signed-off-by: Maxime Austruy <maxime@tralhalla.org>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>