libxl: replace memset() with libxl__device_console_init

The current implementation of libxl__device_console_init does the same
memset() so this is identical for now.

If libxl__device_console_init changes in future (e.g. to prefer a non-zero
default value for some field) then this will continue to work.

Signed-off-by: David Scott <dave.scott@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>

tools/libxl/libxl_create.c

@@ -389,7 +389,7 @@ int libxl__domain_build_info_setdefault(libxl__gc *gc,
 
 static int init_console_info(libxl__device_console *console, int dev_num)
 {
-    memset(console, 0x00, sizeof(libxl__device_console));
+    libxl__device_console_init(console);
     console->devid = dev_num;
     console->consback = LIBXL__CONSOLE_BACKEND_XENCONSOLED;
     console->output = strdup("pty");