drm/xe/tlb: drop unnecessary smp_wmb()

wake_up_all() and wait_event_timeout() already have the correct barriers
as per https://www.kernel.org/doc/Documentation/memory-barriers.txt

.
This should ensure that the seqno_recv write can't be re-ordered wrt to
the actual wake_up_all() i.e we get woken up but there is no write.  The
reader side with wait_event_timeout() also has the correct barriers.
With that drop the hand rolled smp_wmb(), which is anyway missing some
kind of matching barrier on the reader side.

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>