[scsi] Avoid duplicate calls to scsicmd_close()

When a SCSI device is closed in error, the shutdown of the device's
block data interface will probably lead to any outstanding commands
being closed (by whichever object is currently connected to the block
data interface).  However, commands remain in the list of outstanding
commands until the final reference is dropped.  The result is that
scsidev_close() will make a second call to scsicmd_close() for each
command.  This is harmless, but produces confusing debug messages.

Fix by treating the outstanding command list as holding an explicit
reference to each command, and removing the command from the list of
outstanding commands in scsicmd_close().

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

src/drivers/block/scsi.c

 	struct scsi_command *scsicmd =
 		container_of ( refcnt, struct scsi_command, refcnt );
 
-	/* Remove from list of commands */
-	list_del ( &scsicmd->list );
+	/* Drop reference to SCSI device */
 	scsidev_put ( scsicmd->scsidev );
 
 	/* Free command */
 
 	/* 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 );
+	scsicmd_put ( scsicmd );
 }
 
 /**
 	if ( ( rc = scsicmd_command ( scsicmd ) ) != 0 )
 		goto err_command;
 
-	/* Attach to parent interface, mortalise self, and return */
+	/* Attach to parent interface, transfer reference to list, and return */
 	intf_plug_plug ( &scsicmd->block, block );
-	ref_put ( &scsicmd->refcnt );
 	return 0;
 
  err_command:
 			 NULL );
 
 	/* Shut down any remaining commands */
-	list_for_each_entry_safe ( scsicmd, tmp, &scsidev->cmds, list ) {
-		scsicmd_get ( scsicmd );
+	list_for_each_entry_safe ( scsicmd, tmp, &scsidev->cmds, list )
 		scsicmd_close ( scsicmd, rc );
-		scsicmd_put ( scsicmd );
-	}
 }
 
 /** SCSI device block interface operations */