aio_ctx_check: follow CODING_STYLE

replace tab with spaces

Signed-off-by: Cao jin <caoj.fnst@cn.fujitsu.com>
Message-id: 1468501843-14927-1-git-send-email-caoj.fnst@cn.fujitsu.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>