Use DEFINE_SHOW_ATTRIBUTE macro to simplify the code.

Signed-off-by: Qinglang Miao <miaoqinglang@huawei.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20200917125547.104472-1-miaoqinglang@huawei.com


Signed-off-by: Juergen Gross <jgross@suse.com>