libxl: libxl__device_model_version_running should return an int

On error it returns -1 and therefore it needs to return int and not
libxl_device_model_enum. Otherwise gcc 4.6.2 complains:

    libxl.c: In function ‘libxl_domain_suspend’:
    libxl.c:778:9: error: case value ‘4294967295’ not in enumerated type ‘libxl_device_model_version’ [-Werror=switch]

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Ian Campbell <ian.campbell@citrix.com>

tools/libxl/libxl_internal.c

@@ -330,8 +330,7 @@ out:
     return rc;
 }
 
-libxl_device_model_version libxl__device_model_version_running(libxl__gc *gc,
-                                                               uint32_t domid)
+int libxl__device_model_version_running(libxl__gc *gc, uint32_t domid)
 {
     char *path = NULL;
     char *dm_version = NULL;

tools/libxl/libxl_internal.h

@@ -1515,8 +1515,7 @@ _hidden libxl__json_object *libxl__json_parse(libxl__gc *gc, const char *s);
 
   /* Based on /local/domain/$domid/dm-version xenstore key
    * default is qemu xen traditional */
-_hidden libxl_device_model_version
-libxl__device_model_version_running(libxl__gc *gc, uint32_t domid);
+_hidden int libxl__device_model_version_running(libxl__gc *gc, uint32_t domid);
 
 
 /*