staging: most: hdm-usb: Remove invalid reference error

commit e3479f77("staging: most: hdm-usb: Remove create_workqueue()")
cancel_work_sync(&anchor->clear_work_obj) is introduced after freeing
`anchor` causing a invalid reference error. This patch removes this
error by shifting the call to cancel_work_sync before freeing
`anchor`.

Signed-off-by: Amitoj Kaur Chawla <amitoj1606@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>