Clarify wording on allocation

Signed-off-by: David Horstmann <david.horstmann@arm.com>

library/x509.c

diff --git a/library/x509.c b/library/x509.c
index cdc87e5..4035074 100644
--- a/library/x509.c
+++ b/library/x509.c
@@ -469,7 +469,7 @@
  * same set so that they are "merged" together in the functions that consume
  * this list, eg mbedtls_x509_dn_gets().
  *
- * On success, this function allocates a linked list starting at cur->next
+ * On success, this function may allocate a linked list starting at cur->next
  * that must later be free'd by the caller using mbedtls_free(). In error
  * cases, this function frees all allocated memory internally and the caller
  * has no freeing responsibilities.