doc: Fix the Doxygen section endings

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
diff --git a/src/msgb.c b/src/msgb.c
index a403580..c8564db 100644
--- a/src/msgb.c
+++ b/src/msgb.c
@@ -153,4 +153,4 @@
 	tall_msgb_ctx = ctx;
 }
 
-/*! }@ */
+/*! @} */