vfio_pci: fix build on 32-bit systems

We cannot cast directly from pointer to uint64.

Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Alex Barcelo <abarcelo@ac.upc.edu>
Reported-by: NAlex Barcelo <abarcelo@ac.upc.edu>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

hw/vfio_pci.c

@@ -768,7 +768,7 @@ static int vfio_dma_map(VFIOContainer *container, target_phys_addr_t iova,
     struct vfio_iommu_type1_dma_map map = {
         .argsz = sizeof(map),
         .flags = VFIO_DMA_MAP_FLAG_READ,
-        .vaddr = (__u64)vaddr,
+        .vaddr = (__u64)(intptr_t)vaddr,
         .iova = iova,
         .size = size,
     };