Update dhm.h

Minor fix based on review comments
diff --git a/include/mbedtls/dhm.h b/include/mbedtls/dhm.h
index 348d8cf..b3b3761 100644
--- a/include/mbedtls/dhm.h
+++ b/include/mbedtls/dhm.h
@@ -268,7 +268,7 @@
  *                    Byte for PEM data.
  *
  * \return            \c 0 on success.
- * \return            An \c MBEDTLS_ERR_DHM_XXX or MBEDTLS_ERR_PEM_XXX error code
+ * \return            An \c MBEDTLS_ERR_DHM_XXX or \c MBEDTLS_ERR_PEM_XXX error code
  *                    error code on failure.
  */
 int mbedtls_dhm_parse_dhm( mbedtls_dhm_context *dhm, const unsigned char *dhmin,
@@ -283,7 +283,7 @@
  * \param path     The filename to read the DHM parameters from.
  *
  * \return         \c 0 on success.
- * \return            An \c MBEDTLS_ERR_DHM_XXX or MBEDTLS_ERR_PEM_XXX error code
+ * \return            An \c MBEDTLS_ERR_DHM_XXX or \c MBEDTLS_ERR_PEM_XXX error code
  *                    error code on failure.
  */
 int mbedtls_dhm_parse_dhmfile( mbedtls_dhm_context *dhm, const char *path );