Use ARRAY_SIZE macro already defined in linux/kernel.h

Signed-off-by: Ahmed S. Darwish <darwish.07@gmail.com>
Cc: Mikael Starvik <starvik@axis.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>