Changelog entry for ECDSA conversion functions called with bits=0

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/ChangeLog.d/psa_util-bits-0.txt b/ChangeLog.d/psa_util-bits-0.txt
new file mode 100644
index 0000000..9aa70ad
--- /dev/null
+++ b/ChangeLog.d/psa_util-bits-0.txt
@@ -0,0 +1,3 @@
+Bugfix
+   * Fix undefined behavior in some cases when mbedtls_psa_raw_to_der() or
+     mbedtls_psa_der_to_raw() is called with bits=0.