doc: Fix the Doxygen section endings

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
diff --git a/include/osmocom/core/timer.h b/include/osmocom/core/timer.h
index 30f558b..ecb5001 100644
--- a/include/osmocom/core/timer.h
+++ b/include/osmocom/core/timer.h
@@ -82,6 +82,6 @@
 int osmo_timers_update(void);
 int osmo_timers_check(void);
 
-/*! }@ */
+/*! @} */
 
 #endif