rtlwifi: rtl8192cu: Fix false loss of AP indication

A major change in the rtlwifi family recently added code to detect when
there is loss of AP signals. One critical statement needed for the USB
driver was missed.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>