net/hns3: fix flow director error message

There is a coverity defect related "Argument cannot be negative".

This patch fixes it by passing '-ret' to the function strerror() when
ret is negative.

Coverity issue: 349933
Fixes: fcba820d9b ("net/hns3: support flow director")
Cc: stable@dpdk.org

Signed-off-by: Wei Hu (Xavier) <xavier.huwei@huawei.com>

drivers/net/hns3/hns3_fdir.c

@@ -893,7 +893,7 @@ static int hns3_insert_fdir_filter(struct hns3_hw *hw,
 	if (ret < 0) {
 		rte_spinlock_unlock(&fdir_info->flows_lock);
 		hns3_err(hw, "Hash table full? err:%d(%s)!", ret,
-			 strerror(ret));
+			 strerror(-ret));
 		return ret;
 	}