Fix reference to encryption function (#4837)

Author: sy-records

reference/sodium/functions/sodium-crypto-aead-xchacha20poly1305-ietf-decrypt.xml

@@ -32,7 +32,7 @@
     <term><parameter>ciphertext</parameter></term>
     <listitem>
      <para>
-      Must be in the format provided by <function>sodium_crypto_aead_chacha20poly1305_ietf_encrypt</function>
+      Must be in the format provided by <function>sodium_crypto_aead_xchacha20poly1305_ietf_encrypt</function>
       (ciphertext and tag, concatenated).
      </para>
     </listitem>