Yosemite run "mount volumes" is not same as Mountain Lion

Question

I have a script to mount the shared folder from Windows server (named: servicedesk) as a volume in Yosemite iMac.
-- -------begin script-----
set loggedInUser to do shell script "whoami"
tell application "Finder"
  try
  mount volume "smb://servicedesk/M"
  do shell script "ln -sf /Volumes/M/ ~/Desktop/M"
  end try
end tell
----------End script--------
When run the script on Mountain Lion 10.8.5 iMac, I can list the "M" when run the command in terminal: ls /Volumes/
But when run the script on Yosemite iMac, It's show "servicedesk" instead "M" when run the command in terminal: ls /Volumes/
I don't know why it is difference and can't do anything to create symlink to the Desktop now. Please help????
Thank you,

Answer 1

Thanks for your reply @Camelot
Your reply is solved my question.
But I'm still wondering why it is same the way of script done (in OS 10.10.1) with 2 targets: shared folder on iMac and shared folder on Windows. The script which "mount volume" on MAC is have expected result, Windows is not. Please see the picture to easier understand
1/ "Idrive", is mapped from iMAC, "M" is mapped from WIndows
2/ But when show the result in Terminal, "Idrive" can list, "M" doesn't but it's shown "servicedesk". The icon is also difference on the Desktop!!!
much appreciate your comments