Add ChangeLog entry

Signed-off-by: Werner Lewis <werner.lewis@arm.com>
diff --git a/ChangeLog.d/fix-undefined-memcpy-mbedtls_asn1_named_data.txt b/ChangeLog.d/fix-undefined-memcpy-mbedtls_asn1_named_data.txt
new file mode 100644
index 0000000..b30f7fa
--- /dev/null
+++ b/ChangeLog.d/fix-undefined-memcpy-mbedtls_asn1_named_data.txt
@@ -0,0 +1,3 @@
+Bugfix
+   * Fix undefined behavior in mbedtls_asn1_find_named_data(), where val is
+     not NULL and val_len is zero.