swiotlb-xen: add missing xen_dma_map_page call

swiotlb-xen is missing a xen_dma_map_page call in
xen_swiotlb_map_sg_attrs, in the bounce buffer path.
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/xen/swiotlb-xen.c

@@ -555,6 +555,11 @@ xen_swiotlb_map_sg_attrs(struct device *hwdev, struct scatterlist *sgl,
 				sg_dma_len(sgl) = 0;
 				return 0;
 			}
+			xen_dma_map_page(hwdev, pfn_to_page(map >> PAGE_SHIFT),
+						map & ~PAGE_MASK,
+						sg->length,
+						dir,
+						attrs);
 			sg->dma_address = xen_phys_to_bus(map);
 		} else {
 			/* we are not interested in the dma_addr returned by