ntlm: improve comment for encrypt_des

Reported-by: Andrei Rybak
Fixes #9903
Closes #9925

lib/curl_ntlm_core.c

@@ -186,9 +186,9 @@ static void setup_des_key(const unsigned char *key_56,
 #elif defined(USE_NSS)
 
 /*
- * Expands a 56 bit key KEY_56 to 64 bit and encrypts 64 bit of data, using
- * the expanded key.  The caller is responsible for giving 64 bit of valid
- * data is IN and (at least) 64 bit large buffer as OUT.
+ * encrypt_des() expands a 56 bit key KEY_56 to 64 bit and encrypts 64 bit of
+ * data, using the expanded key. IN should point to 64 bits of source data,
+ * OUT to a 64 bit output buffer.
  */
 static bool encrypt_des(const unsigned char *in, unsigned char *out,
                         const unsigned char *key_56)