Fixes the following sparse warning:

drivers/net/ethernet/mellanox/mlxsw/spectrum_qdisc.c:464:1: warning:
 symbol 'mlxsw_sp_qdisc_prio_unoffload' was not declared. Should it be static?
Signed-off-by: NWei Yongjun <weiyongjun1@huawei.com>
Acked-by: NJiri Pirko <jiri@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>