vmwgfx: corruption in vmw_event_fence_action_create()

We don't allocate enough data for this struct.  As soon as we start
modifying event->event on the next lines, then we're going beyond the
end of the memory we allocated.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
cc: stable@vger.kernel.org
Signed-off-by: Dave Airlie <airlied@gmail.com>