cxgb4: make function 'cxgb4_mqprio_free_hw_resources' static

Fix sparse warnings:

drivers/net/ethernet/chelsio/cxgb4/cxgb4_tc_mqprio.c:242:6: warning: symbol 'cxgb4_mqprio_free_hw_resources' was not declared. Should it be static?

Reported-by: Hulk Robot <hulkci@huawei.com>
Fixes: 2d0cb84d ("cxgb4: add ETHOFLD hardware queue support")
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>