* disk/ata.c (grub_ata_pio_read): Don't wait for the command to
become activate.
(grub_ata_pio_write): Likewise.
(grub_atapi_identify): Wait after issuing an ATA command.
(grub_atapi_packet): Likewise.
(grub_ata_identify): Likewise.
(grub_ata_readwrite): Likewise.
* disk/ata.c (grub_ata_pio_read): Detect and return the error code.
(grub_ata_pio_write): Likewise.
(grub_ata_readwrite): Use `grub_error', instead of
returning `grub_errno'.