First, let me say I have not used hostfs or UML, but I'll try to help.
Are you attempting to do this mount on a UML (User-Mode Linux) virtual machine? If not, that may be the problem; hostfs is not one of the standard mount options for Linux (try 'man mount' on your system, scrolling down to the -t options, to be sure), but exists as a mount option in UML.
If you are not using UML and you just want to create an alternative location for a directory, use a symbolic link:
ln -s /home/imada_login/Desktop /mnt/tmp
Later on, when you wish, you can unlink it with: