Fix error handling in rand_drbg_new

Reviewed-by: NMatthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
Reviewed-by: NPaul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/7519)

crypto/rand/drbg_lib.c

@@ -234,10 +234,7 @@ static RAND_DRBG *rand_drbg_new(int secure,
     return drbg;
 
  err:
-    if (drbg->secure)
-        OPENSSL_secure_free(drbg);
-    else
-        OPENSSL_free(drbg);
+    RAND_DRBG_free(drbg);
 
     return NULL;
 }