scsi: target: spc: Fix RSOC parameter data header size

The SPC document states that "The COMMAND DATA LENGTH field indicates the
length in bytes of the command descriptor list".

The length should be subtracted by 4 to represent the length of the
description list, not 3.

Signed-off-by: Chaohai Chen <wdhh66@163.com>
Link: https://lore.kernel.org/r/20250115070739.216154-1-wdhh66@163.com


Reviewed-by: Dmitry Bogdanov <d.bogdanov@yadro.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>