ide: remove hw_regs_t typedef

Remove hw_regs_t typedef and rename struct hw_regs_s to struct ide_hw.

There should be no functional changes caused by this patch.

Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>