rtl8192cu: Fix for rtlwifi's bluetooth coexist functionality

Initialize function pointer with a function indicating bt coexist is not there.
Prevents Ooops.

Signed-off-by: Karsten Wiese <fzuuzf@googlemail.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>