scsi: target: Remove incorrect zero blocks WRITE_SAME check

We use WSNZ=1 so if we get a WRITE_SAME with zero logical blocks we are
supposed to fail it. We do this check and failure in target_core_sbc.c
before calling into the backend, so we can remove the incorrect check in
target_core_file.

Link: https://lore.kernel.org/r/20220628200230.15052-2-michael.christie@oracle.com
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>