cxgb4: Make t4_get_tp_e2c_map static

Fix sparse warning:

drivers/net/ethernet/chelsio/cxgb4/t4_hw.c:6216:14:
 warning: symbol 't4_get_tp_e2c_map' was not declared. Should it be static?

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>