net: ethernet: ti: cpsw: remove priv from cpsw_get_slave_port() parameters list

There is no need in priv here.

Reviewed-by: Mugunthan V N <mugunthanvnm@ti.com>
Reviewed-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>