Fix position_t

git-svn-id: https://redmine.imt-atlantique.fr/svn/xaal/schemas/branches/schemas-0.7@2454 b32b6428-25c9-4566-ad07-03861ab6144f

shutter.position

@@ -26,7 +26,7 @@
     }
   },
   "datamodel": {
-    "position": {
+    "position_t": {
       "description": "Level of aperture of the shutter",
       "unit": "%",
       "type": "data = (0..100) / (0.0..100.0)"