[scsi] Avoid duplicate call to scsicmd_close() on TEST UNIT READY failure

When the TEST UNIT READY command receives an error response, the
shutdown of the command's block data interface will result in
scsidev_ready() closing the SCSI device.  This will subsequently
result in a duplicate call to scsicmd_close(), leading to an assertion
failure when list_del() is called for the second time.

Fix by removing the command from the list of outstanding commands
before shutting down the command's interfaces.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/block/scsi.c

 		       scsidev, scsicmd->tag, strerror ( rc ) );
 	}
 
+	/* Remove from list of commands */
+	list_del ( &scsicmd->list );
+
 	/* Shut down interfaces */
 	intfs_shutdown ( rc, &scsicmd->scsi, &scsicmd->block, NULL );
 
-	/* Remove from list of commands and drop list's reference */
-	list_del ( &scsicmd->list );
+	/* Drop list's reference */
 	scsicmd_put ( scsicmd );
 }