Correct english in changelog.

Signed-off-by: Paul Elliott <paul.elliott@arm.com>
diff --git a/ChangeLog.d/fix_psa_crypto_leak.txt b/ChangeLog.d/fix_psa_crypto_leak.txt
index 5add73d..6f9e5fe 100644
--- a/ChangeLog.d/fix_psa_crypto_leak.txt
+++ b/ChangeLog.d/fix_psa_crypto_leak.txt
@@ -1,2 +1,2 @@
 Bugfix
-   * Fix memory leak that occured in error case in psa_generate_derived_key_internal()
+   * Fix a memory leak in an error case in psa_generate_derived_key_internal().