doc: Fix the Doxygen section endings

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
diff --git a/include/osmocom/gsm/a5.h b/include/osmocom/gsm/a5.h
index 7e6a17c..649dbab 100644
--- a/include/osmocom/gsm/a5.h
+++ b/include/osmocom/gsm/a5.h
@@ -58,6 +58,6 @@
 void osmo_a5_1(const uint8_t *key, uint32_t fn, ubit_t *dl, ubit_t *ul);
 void osmo_a5_2(const uint8_t *key, uint32_t fn, ubit_t *dl, ubit_t *ul);
 
-/*! }@ */
+/*! @} */
 
 #endif /* __OSMO_A5_H__ */