hw/ppc/spapr_iommu: Fix the check for invalid upper bits in liobn

The check "liobn & 0xFFFFFFFF00000000ULL" in spapr_tce_find_by_liobn()
is completely useless since liobn is only declared as an uint32_t
parameter. Fix this by using target_ulong instead (this is what most
of the callers of this function are using, too).

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>
