rtlwifi: rtl8192cu: Fix problem that prevents reassociation

The driver was failing to clear the BSSID when a disconnect happened. That
prevented a reconnection. This problem is reported at
https://bugzilla.redhat.com/show_bug.cgi?id=789605,
https://bugzilla.redhat.com/show_bug.cgi?id=866786,
https://bugzilla.redhat.com/show_bug.cgi?id=906734, and
https://bugzilla.kernel.org/show_bug.cgi?id=46171

.

Thanks to Jussi Kivilinna for making the critical observation
that led to the solution.

Reported-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>
Tested-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>
Tested-by: Alessandro Lannocca <alessandro.lannocca@gmail.com>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Stable <stable@vger.kernel.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>