[PATCH] sysfs: if show/store is missing return -EIO

sysfs: if attribute does not implement show or store method
       read/write should return -EIO instead of 0 or -EINVAL.

Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>