Exporting world writable sysfs/debugfs files is usually a bad thing.  Warn
about it.

Signed-off-by: Dave Jones <davej@redhat.com>
Cc: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>