rtl8192cu: fix the mesh beaconing

Patch "rtlwifi: add support to send beacon frame" allows
the beaconing of rtl8192cu. But mesh beaconing is not
working. Fix this.

Signed-off-by: Chun-Yeow Yeoh <yeohchunyeow@gmail.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>