iris: fix the order of src and dst for fence memcpy

This fixes random failures with "deqp-egl --deqp-case=*multithread*":
   iris: Failed to submit batchbuffer: No such file or directory

Fixes: 6b1a56b908 ("iris: Drop stale syncobj references in fence_server_sync")
Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7289>

src/gallium/drivers/iris/iris_fence.c

@@ -154,7 +154,7 @@ clear_stale_syncobjs(struct iris_batch *batch)
 
       if (syncobj != nth_syncobj) {
          *syncobj = *nth_syncobj;
-         memcpy(nth_fence, fence, sizeof(*fence));
+         memcpy(fence, nth_fence, sizeof(*fence));
       }
    }
 }