first get a wheel alignment done and see whether this can be rectified by adjusting rack end lengths.
If it fails, inspect the rack to see whether rack is mis aligned due to some reason.
If not most probable cause is, someone adjusted the center position of the steering rack during a repair. usually the teething of the rack wears out fast from the center position, therefore as a remedy mechanics do shift the center postion of the rack by couple of teeth and adjust the rack ends accordingly.
harshansenadhir's post in Daihatsu Charade Power Steering Issue was marked as the answer