Use DEFINE_SEQ_ATTRIBUTE macro to simplify the code.

Link: https://lore.kernel.org/r/20200916025030.3992991-1-liushixin2@huawei.comSigned-off-by: Liu Shixin <liushixin2@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>