CURLOPT_READFUNCTION.3: refer to argument with correct name

Bug: #2175

[ci skip]

docs/libcurl/opts/CURLOPT_READFUNCTION.3

@@ -5,7 +5,7 @@
 .\" *                            | (__| |_| |  _ <| |___
 .\" *                             \___|\___/|_| \_\_____|
 .\" *
-.\" * Copyright (C) 1998 - 2015, Daniel Stenberg, <daniel@haxx.se>, et al.
+.\" * Copyright (C) 1998 - 2017, Daniel Stenberg, <daniel@haxx.se>, et al.
 .\" *
 .\" * This software is licensed as described in the file COPYING, which
 .\" * you should have received as part of this distribution. The terms
@@ -36,7 +36,7 @@ Pass a pointer to your callback function, as the prototype shows above.
 This callback function gets called by libcurl as soon as it needs to read data
 in order to send it to the peer - like if you ask it to upload or post data to
 the server. The data area pointed at by the pointer \fIbuffer\fP should be
-filled up with at most \fIsize\fP multiplied with \fInmemb\fP number of bytes
+filled up with at most \fIsize\fP multiplied with \fInitems\fP number of bytes
 by your function.
 
 Your function must then return the actual number of bytes that it stored in