GCS_MAVLink: fixed corruption of FTP reply component ID

this led to not being able to do FTP transfers with
support.ardupilot.org unless MissionPlanner used the same component ID
as the support engineer GCS

libraries/GCS_MAVLink/GCS_FTP.cpp

@@ -169,7 +169,7 @@ void GCS_MAVLINK::ftp_worker(void) {
         }
 
         // if it's a rerequest and we still have the last response then send it
-        if ((request.sysid == reply.sysid) && (request.compid = reply.compid) &&
+        if ((request.sysid == reply.sysid) && (request.compid == reply.compid) &&
             (request.session == reply.session) && (request.seq_number + 1 == reply.seq_number)) {
             ftp_push_replies(reply);
             continue;