cifs-utils: revert back to version 5.6

The updated version 5.9 couldn't mount any of my shares:

  Status code returned 0xc000006d NT_STATUS_LOGON_FAILURE
  CIFS VFS: Send error in SessSetup = -13
  CIFS VFS: cifs_mount failed w/return code = -13

Apparently, this is a known problem in Windows Vista that needs to be
fixed on the server side. :-(