contexthub_hal: fix comment

Change-Id: I98c88fce7414145a493778ca349438fd0ab36b2b
diff --git a/include/hardware/context_hub.h b/include/hardware/context_hub.h
index 01d2377..f026b08 100644
--- a/include/hardware/context_hub.h
+++ b/include/hardware/context_hub.h
@@ -262,7 +262,7 @@
 
     /**
      * Enumerate all available hubs.The list is returned in "list".
-     * @return result : 0 if successful, error code otherwise
+     * @return result : number of hubs in list or error  (negative)
      *
      * This method shall be called at device bootup.
      */