vduse: Fix returning wrong type in vduse_domain_alloc_iova()

This fixes the following smatch warnings:

drivers/vdpa/vdpa_user/iova_domain.c:305 vduse_domain_alloc_iova() warn: should 'iova_pfn << shift' be a 64 bit type?

Fixes: 8c773d5 ("vduse: Implement an MMU-based software IOTLB")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
Link: https://lore.kernel.org/r/20220121083940.102-1-xieyongji@bytedance.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>

drivers/vdpa/vdpa_user/iova_domain.c

@@ -294,7 +294,7 @@ vduse_domain_alloc_iova(struct iova_domain *iovad,
 
 	iova_pfn = alloc_iova_fast(iovad, iova_len, limit >> shift, true);
 
-	return iova_pfn << shift;
+	return (dma_addr_t)iova_pfn << shift;
 }
 
 static void vduse_domain_free_iova(struct iova_domain *iovad,