misdn: one handmade ARRAY_SIZE converted

Defined as:

static struct device_attribute element_attributes[] = {

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Karsten Keil <kkeil@suse.de>