ORB_PRIO: set ORB_PRIO_MIN to 1 instead of 0

This is needed as the sensors app assumes a value of 0 means uninitialized.

Follow-up to 'Sensors app: Fix consistency checks', a6696d33

src/modules/uORB/uORB.h

@@ -68,7 +68,7 @@ typedef const struct orb_metadata *orb_id_t;
  * Relevant for multi-topics / topic groups
  */
 enum ORB_PRIO {
-	ORB_PRIO_MIN = 0,
+	ORB_PRIO_MIN = 1, // leave 0 free for other purposes, eg. marking an uninitialized value
 	ORB_PRIO_VERY_LOW = 25,
 	ORB_PRIO_LOW = 50,
 	ORB_PRIO_DEFAULT = 75,