i965: Assert the execobject handles match for this device

Object handles are local to the device fd, so double check we are not
mixing together objects from multiple screens on execbuf submission.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/i965/intel_batchbuffer.c

@@ -188,6 +188,8 @@ intel_batchbuffer_init(struct brw_context *brw)
 static unsigned
 add_exec_bo(struct intel_batchbuffer *batch, struct brw_bo *bo)
 {
+   assert(bo->bufmgr == batch->batch.bo->bufmgr);
+
    unsigned index = READ_ONCE(bo->index);
 
    if (index < batch->exec_count && batch->exec_bos[index] == bo)