stats: Add OSMO prefix to STAT_ITEM_NOVALUE_ID

This symbol is globally visible and therefore should have an OSMO
prefix like the other identifiers exported by stat_item.h.

Sponsored-by: On-Waves ehf
diff --git a/src/stat_item.c b/src/stat_item.c
index a6a8481..fcd6781 100644
--- a/src/stat_item.c
+++ b/src/stat_item.c
@@ -105,7 +105,7 @@
 
 		for (i = 0; i <= item->last_offs; i++) {
 			item->values[i].value = desc->item_desc[item_idx].default_value;
-			item->values[i].id = STAT_ITEM_NOVALUE_ID;
+			item->values[i].id = OSMO_STAT_ITEM_NOVALUE_ID;
 		}
 	}
 
@@ -128,7 +128,7 @@
 		item->last_offs = 0;
 
 	global_value_id += 1;
-	if (global_value_id == STAT_ITEM_NOVALUE_ID)
+	if (global_value_id == OSMO_STAT_ITEM_NOVALUE_ID)
 		global_value_id += 1;
 
 	item->values[item->last_offs].value = value;
@@ -147,7 +147,7 @@
 	next_value = &item->values[next_offs];
 
 	while (next_value->id - *next_idx >= 0 &&
-		next_value->id != STAT_ITEM_NOVALUE_ID)
+		next_value->id != OSMO_STAT_ITEM_NOVALUE_ID)
 	{
 		item_value = next_value;