ide-cs: fix probing and add warm-plug support

* Fix probing by using ide_port_scan() and moving "retry loop"
  from ide_config() to idecs_register().

* Don't fail probe if there are no devices attached to a port.

* Remove (now redundant) error message from ide_config().

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>