scsi: snic: Convert to DEFINE_SHOW_ATTRIBUTE()

Use DEFINE_SHOW_ATTRIBUTE() macro to simplify the code.

Link: https://lore.kernel.org/r/20210331065326.18804-1-dingsenjie@163.com


Signed-off-by: dingsenjie <dingsenjie@yulong.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>