e1000: Use ARRAY_SIZE macro when appropriate

A patch to use ARRAY_SIZE macro already defined in kernel.h.

Signed-off-by: Ahmed S. Darwish <darwish.07@gmail.com>
Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>