ray_cs: replace del_timer by del_timer_sync

Use del_timer_sync to ensure that the timer is stopped on all CPUs before
the driver exits.

This change was suggested by Thomas Gleixner.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/

)

// <smpl>
@r@
identifier i,t,ex;
@@
struct t i = { .remove = ex, };

@@
identifier r.ex;
@@
ex(...) {
  <...
- del_timer
+ del_timer_sync
    (...)
  ...>
}
// </smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: John W. Linville <linville@tuxdriver.com>