Update comments

Signed-off-by: Pengyu Lv <pengyu.lv@arm.com>
diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index 894167a..5455fa2 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -1378,9 +1378,9 @@
     defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_RSA_PUBLIC_KEY)
         case PSA_KEY_TYPE_RSA_KEY_PAIR:
         case PSA_KEY_TYPE_RSA_PUBLIC_KEY:
-            /* TODO: reporting the public exponent for opaque keys
-             * is not yet implemented.
-             * https://github.com/ARMmbed/mbed-crypto/issues/216
+            /* TODO: This is a temporary situation where domain parameters are deprecated,
+             * but we need it for namely generating an RSA key with a non-default exponent.
+             * This would be improved after https://github.com/Mbed-TLS/mbedtls/issues/6494.
              */
             if (!psa_key_lifetime_is_external(slot->attr.lifetime)) {
                 mbedtls_rsa_context *rsa = NULL;