doc: Fix the Doxygen section endings

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
diff --git a/src/serial.c b/src/serial.c
index bc64b8a..11ba503 100644
--- a/src/serial.c
+++ b/src/serial.c
@@ -226,4 +226,4 @@
 	return 0;
 }
 
-/*! }@ */
+/*! @} */