target: Generate failure for XCOPY I/O with non-zero scsi_status

This patch adds the missing non-zero se_cmd->scsi_status check required
for local XCOPY I/O within target_xcopy_issue_pt_cmd() to signal an
exception case failure.

This will trigger the generation of SAM_STAT_CHECK_CONDITION status
from within target_xcopy_do_work() process context code.
Reported-by: Thomas Glanzmann <thomas@glanzmann.de>
Reported-by: Douglas Gilbert <dgilbert@interlog.com>
Cc: Thomas Glanzmann <thomas@glanzmann.de>
Cc: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_xcopy.c

@@ -679,7 +679,8 @@ static int target_xcopy_issue_pt_cmd(struct xcopy_pt_cmd *xpt_cmd)
 
 	pr_debug("target_xcopy_issue_pt_cmd(): SCSI status: 0x%02x\n",
 			se_cmd->scsi_status);
-	return 0;
+
+	return (se_cmd->scsi_status) ? -EINVAL : 0;
 }
 
 static int target_xcopy_read_source(