staging: rtl8723bs: Fix Unneeded variable: "ret". Return "0"

coccicheck reported Unneeded variable ret at rtl8723bs/core/rtw_ap.c:1400.
Function "rtw_acl_remove_sta" always returns 0. Modified return type of the
function to void.

Signed-off-by: Shobhit Kukreti <shobhitkukreti@gmail.com>
Reviewed-by: Bastien Nocera <hadess@hadess.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>