[SCSI] sd: Return correct error code for DIF

sd_dif.c was not updated to return -EILSEQ, leading to error handling
failures in applications which provide their own integrity metadata (as
opposed to being protected by the block layer functions).

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>