libweston: fix typos

Signed-off-by: Maxime Roussin-Bélanger <maxime.roussinbelanger@gmail.com>
diff --git a/libweston/timeline.c b/libweston/timeline.c
index d5738f4..7b6f25c 100644
--- a/libweston/timeline.c
+++ b/libweston/timeline.c
@@ -362,7 +362,7 @@
  * Can be used from outside libweston.
  *
  * @param wc a weston_compositor instance
- * @param object the underyling object
+ * @param object the underlying object
  *
  * @ingroup log
  */