libxendevicemodel: initialise extent.pad to zero

The pad field needs to be zero as required by the hypervisor.

Instead of setting the pad separately, use C99 initialiser.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>

tools/libs/devicemodel/core.c

@@ -483,10 +483,10 @@ int xendevicemodel_modified_memory(
     xendevicemodel_handle *dmod, domid_t domid, uint64_t first_pfn,
     uint32_t nr)
 {
-    struct xen_dm_op_modified_memory_extent extent;
-
-    extent.first_pfn = first_pfn;
-    extent.nr = nr;
+    struct xen_dm_op_modified_memory_extent extent = {
+        .first_pfn = first_pfn,
+        .nr = nr,
+    };
 
     return xendevicemodel_modified_memory_bulk(dmod, domid, &extent, 1);
 }