consttime flag changed

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Kurt Roeckx <kurt@roeckx.be>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from openssl#5170)

Author: Samuel Weiser

crypto/rsa/rsa_gen.c

@@ -89,7 +89,7 @@ static int rsa_builtin_keygen(RSA *rsa, int bits, BIGNUM *e_value,
     if (BN_copy(rsa->e, e_value) == NULL)
         goto err;
 
-    BN_set_flags(rsa->e, BN_FLG_CONSTTIME);
+    BN_set_flags(r2, BN_FLG_CONSTTIME);
     /* generate p and q */
     for (;;) {
         if (!BN_generate_prime_ex(rsa->p, bitsp, 0, NULL, NULL, cb))