rocker: fix compile error in _flow_match

hw/net/rocker/rocker_flow.c: In function ‘_flow_match’:
hw/net/rocker/rocker_flow.c:368:47: error: suggest braces around empty body in an ‘if’ statement [-Werror=empty-body]
         flow_key_dump(&flow->key, &flow->mask);
                                               ^
cc1: all warnings being treated as errors

Signed-off-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Scott Feldman <sfeldma@gmail.com>