hinic: make symbol 'dump_mox_reg' static

Fix sparse warnings:

drivers/net/ethernet/huawei/hinic/hinic_hw_mbox.c:601:6: warning: symbol 'dump_mox_reg' was not declared. Should it be static?
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zheng Bin <zhengbin13@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/huawei/hinic/hinic_hw_mbox.c

@@ -598,7 +598,7 @@ static void write_mbox_msg_attr(struct hinic_mbox_func_to_func *func_to_func,
 			     HINIC_FUNC_CSR_MAILBOX_CONTROL_OFF, mbox_ctrl);
 }
 
-void dump_mox_reg(struct hinic_hwdev *hwdev)
+static void dump_mox_reg(struct hinic_hwdev *hwdev)
 {
 	u32 val;