net: hns3: fix a wrong checking in the hclge_tx_buffer_calc()

Only the TC is enabled, we need to check whether the buffer is enough,
otherwise it may lead to a wrong -ENOMEM case.

Fixes: 9ffe79a9 ("net: hns3: Support for dynamically assigning tx buffer to TC")
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>