ide: remove SATA_*_REG macros

* siimage.c: use hwif->sata_scr[SATA_{ERROR,STATUS}_OFFSET] instead of
  SATA_{ERROR,STATUS}_REG macros.

* Remove no longer needed SATA_*_REG macros.

While at it:

* Remove needless SATA Status register read from sil_sata_reset_poll().

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