ide: use ->tf_read in ide_read_error()

* Add IDE_TFLAG_IN_FEATURE taskfile flag for reading Feature
  register and handle it in ->tf_read.

* Convert ide_read_error() to use ->tf_read instead of ->INB,
  then uninline and export it.

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