Add Changelog entry

Signed-off-by: Aditya Deshpande <aditya.deshpande@arm.com>
diff --git a/ChangeLog.d/fix_dh_genprime_error_reporting.txt b/ChangeLog.d/fix_dh_genprime_error_reporting.txt
new file mode 100644
index 0000000..1c98947
--- /dev/null
+++ b/ChangeLog.d/fix_dh_genprime_error_reporting.txt
@@ -0,0 +1,4 @@
+Bugfix
+   * Fix bug in error reporting in dh_genprime.c where upon failure,
+     the error code returned by mbedtls_mpi_write_file() is overwritten
+     and therefore not printed.