staging: speakup: Replace del_timer with del_timer_sync

Use del_timer_sync to ensure timer is stopped on all CPUs before
the driver exists and the timer should not run when the module is
being removed. Since the timer is not called from an interrupt
context, this change is safe and will not cause deadlock.

The Coccinelle semantic patch used to make this change is as
follows:
// <smpl>
@r@
declarer name module_exit;
identifier ex;
@@

module_exit(ex);

@@
identifier r.ex;
@@

ex(...) {
  <...
- del_timer
+ del_timer_sync
    (...)
  ...>
}
// </smpl>

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