Update lib/cifra/chacha20.c

Co-authored-by: Kazuho Oku <kazuhooku@gmail.com>
diff --git a/lib/cifra/chacha20.c b/lib/cifra/chacha20.c
index 03b06db..fe19c32 100644
--- a/lib/cifra/chacha20.c
+++ b/lib/cifra/chacha20.c
@@ -193,7 +193,7 @@
     struct chacha20poly1305_context_t *ctx = (struct chacha20poly1305_context_t *)_ctx;
 
     ctx->super.dispose_crypto = chacha20poly1305_dispose_crypto;
-    ctx->super.do_xor_iv = minicrypto_chacha20_aead_xor_iv;
+    ctx->super.do_xor_iv = chacha20poly1305_xor_iv;
     if (is_enc) {
         ctx->super.do_encrypt_init = chacha20poly1305_init;
         ctx->super.do_encrypt_update = chacha20poly1305_encrypt_update;