It is more clear to use DEFINE_DEBUGFS_ATTRIBUTE to define debugfs file
operation rather than DEFINE_SIMPLE_ATTRIBUTE.

Signed-off-by: zhong jiang <zhongjiang@huawei.com>
Acked-by: Jakub Kicinski <kubakici@wp.pl>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>