net: hns3: change the method of getting cmd index in debugfs

Currently, the cmd index is obtained in debugfs by comparing file names.
However, this method may cause errors when processing more complex file
names. So, change this method by saving cmd in private data and comparing
it when getting cmd index in debugfs for optimization.

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: Jakub Kicinski <kuba@kernel.org>