[PATCH] Fix RAID5 + IA64 compile

CONFIG_MD_RAID5 became CONFIG_MD_RAID456 in drivers/md/Kconfig.  Make
the same change in arch/ia64

Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: Aron Griffis <aron@hp.com>
Acked-by: Jes Sorenson <jes@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>