Impact: cleanup, remove last user of set_pte_present

set_pte_vaddr() is only used to install ptes in fixmaps, and
should never be used to overwrite a present mapping.
Signed-off-by: NJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Xen-devel <xen-devel@lists.xensource.com>
LKML-Reference: <1237406613-2929-1-git-send-email-jeremy@goop.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>