hw/ppc/virtex_ml507:fix leak of fdevice tree blob

The device tree blob returned by load_device_tree is malloced.
We should free it after cpu_physical_memory_write().
Reported-by: NEuler Robot <euler.robot@huawei.com>
Signed-off-by: NChen Qun <kuhn.chenqun@huawei.com>
Message-Id: <20200218091154.21696-3-kuhn.chenqun@huawei.com>
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>

hw/ppc/virtex_ml507.c

@@ -188,6 +188,7 @@ static int xilinx_load_device_tree(hwaddr addr,
     if (r < 0)
         fprintf(stderr, "couldn't set /chosen/bootargs\n");
     cpu_physical_memory_write(addr, fdt, fdt_size);
+    g_free(fdt);
     return fdt_size;
 }