[IA64] don't double >> PAGE_SHIFT pointer for /dev/kmem access

Don't PAGE_SHIFT pointer before handing it to virt_to_page() in
xlate_dev_kmem_ptr() as it results in a double shift.

Spotted by Bob Montgomery.

Signed-off-by: Jes Sorensen <jes@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>