VT-d: change bogus return value of intel_iommu_lookup_page()

VT-d: change bogus return value of intel_iommu_lookup_page()

The function passes 0 as "alloc" argument to addr_to_dma_page_maddr(),
so -ENOMEM simply makes no sense (and its use was probably simply a
copy-and-paste effect originating at intel_iommu_map_page()).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>