staging: r8188eu: Fix smatch warning in core/rtw_wlan_util.c

A misplaced _func_exit_ macro leads to the following smatch warning:
drivers/staging/rtl8188eu/core/rtw_wlan_util.c:1105 rtw_check_bcn_info() info: ignoring unreachable code.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>