Applied some advices of Marco Elver on atomic usage of Debugfs,
which is carried out by basing on Arnd Bergmann's fixing patch.
Reported-by: NArnd Bergmann <arnd@arndb.de>
Reported-by: NMarco Elver <elver@google.com>
Signed-off-by: NZaibo Xu <xuzaibo@huawei.com>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>