Add changelog entry for x509 cert_req null dereference fix

Signed-off-by: Waleed Elmelegy <waleed.elmelegy@arm.com>
diff --git a/ChangeLog.d/fix-issue-x509-cert_req.txt b/ChangeLog.d/fix-issue-x509-cert_req.txt
new file mode 100644
index 0000000..7e4effd
--- /dev/null
+++ b/ChangeLog.d/fix-issue-x509-cert_req.txt
@@ -0,0 +1,2 @@
+Bugfix
+   * Fix possible NULL dereference issue in X509 cert_req program if an entry in the san parameter is not separated by a colon.