scsi: target: drop xcopy DISK BLOCK LENGTH debug

The DISK BLOCK LENGTH field is carried with XCOPY target descriptors on the
wire, but is currently unmarshalled during 0x02 segment descriptor
passing. The unmarshalled value is currently unused, so drop it.

Link: https://lore.kernel.org/r/20200327141954.955-3-ddiss@suse.de


Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David Disseldorp <ddiss@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>