virtio_balloon: fix PFN format for virtio-1

BugLink: http://bugs.launchpad.net/bugs/1592042



Everything should be LE when using virtio-1, but
the linux balloon driver does not seem to care about that.

Reported-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
(cherry picked from commit 87c9403b)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Acked-by: Christopher Arges <chris.j.arges@canonical.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>