net: hns3: fix race condition in debugfs

When multiple threads concurrently access the debugfs content, data
and pointer exceptions may occur. Therefore, mutex lock protection is
added for debugfs.

Fixes: 5e69ea7e ("net: hns3: refactor the debugfs process")
Signed-off-by: Yufeng Mo <moyufeng@huawei.com>
Signed-off-by: Guangbin Huang <huangguangbin2@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>